Curing Agent Resin Explained: Key Specifications, Features, and Common Uses

Types of Curing Agent Resin

A curing agent resin, also known as a hardener, plays a crucial role in the polymerization process of thermosetting resins—particularly epoxy systems. These agents initiate and control the chemical reaction that transforms liquid resins into solid, durable materials. The choice of curing agent significantly affects the final product’s mechanical strength, thermal stability, chemical resistance, and application suitability.

Each type of curing agent is engineered for specific performance requirements and environmental conditions. Below is a detailed breakdown of the most common types, their characteristics, advantages, limitations, and ideal applications.

Aromatic Amine Hardeners

Known for exceptional thermal and chemical resistance, aromatic amines are widely used in high-performance epoxy systems.

Advantages

• Superior heat resistance (up to 200°C+)
• Excellent chemical and solvent resistance
• High cross-link density for structural integrity
• Ideal for demanding industrial environments

Limitations

• Poor UV resistance (can yellow or degrade)
• Slower cure at room temperature
• Higher toxicity; requires protective handling

Best for: Aerospace composites, electronic encapsulation, high-temp adhesives

Aliphatic Amine Hardeners

Offer fast curing at ambient temperatures with good mechanical properties and UV stability.

Advantages

• Rapid cure even at low temperatures
• Good adhesion to various substrates
• Resistant to yellowing under UV exposure
• Lower viscosity for easy mixing and application

Limitations

• Moderate heat resistance (typically below 120°C)
• Less chemical resistance than aromatic types
• Strong odor and moisture sensitivity during cure

Best for: Marine coatings, construction adhesives, garage floor sealants

Polyamine Hardeners

These multi-functional amines enhance cross-linking and improve toughness and durability in epoxy systems.

Advantages

• Accelerated curing without external heat
• High degree of cross-linking for improved strength
• Good flexibility and impact resistance
• Versatile in both coatings and structural applications

Limitations

• Can be brittle if over-cured
• Sensitive to humidity during application
• May require pot-life management in large batches

Best for: High-performance composites, industrial floor coatings, tank linings

Phenolic Curing Agents

Used in combination with epoxy resins for extreme temperature and fire resistance.

Advantages

• Outstanding thermal stability (up to 250°C)
• Excellent flame and arc resistance
• High chemical and creep resistance
• Forms rigid, dimensionally stable thermosets

Limitations

• Brittle nature limits impact resistance
• Requires high-temperature curing cycles
• Dark color restricts aesthetic applications

Best for: Electrical insulation, aerospace components, high-temp industrial parts

Polyacid Curing Agents

Cationic systems that enable curing in challenging environments, including moisture-rich conditions.

Advantages

• Effective curing in wet or humid environments
• Superior moisture and chemical resistance
• Low shrinkage during polymerization
• Ideal for underwater or offshore applications

Limitations

• Limited compatibility with some resin systems
• Requires precise formulation control
• Higher cost compared to amine-based systems

Best for: Marine coatings, oil & gas pipeline linings, submerged structures

Type	Heat Resistance	Cure Speed	Chemical Resistance	Best Application
Aromatic Amine	Excellent (180–200°C)	Slow to Moderate	Excellent	Aerospace, electronics, high-temp adhesives
Aliphatic Amine	Moderate (80–120°C)	Fast	Good	Coatings, marine, construction
Polyamine	Good (100–150°C)	Fast	Very Good	Floor coatings, composites, sealants
Phenolic	Exceptional (200–250°C)	Slow (requires heat)	Excellent	Electrical, insulation, industrial components
Polyacid (Cationic)	Good (120–160°C)	Moderate	Excellent	Marine, oil & gas, humid environments

Expert Tip: Always consider the operating environment—temperature, moisture, UV exposure, and chemical contact—when selecting a curing agent. Mismatched hardeners can lead to premature failure, reduced adhesion, or compromised structural integrity.

Key Selection Criteria

• Temperature Requirements: High-temp applications demand aromatic amines or phenolic systems.
• Environmental Exposure: UV stability favors aliphatic amines; moisture resistance favors polyacid systems.
• Cure Conditions: Field applications often require ambient-cure systems like aliphatic or polyamines.
• Safety & Handling: Aromatic amines require ventilation and PPE due to toxicity concerns.

Features of Curing Agent Resin

A two-part epoxy resin kit is a versatile and widely used material system composed of a resin and a curing agent (also known as a hardener). The unique features of the curing agent play a decisive role in determining the final performance, durability, and suitability of the cured epoxy for specific industrial, commercial, and DIY applications. Understanding these features enables users to select the optimal formulation for their needs—whether it's for high-strength bonding, protective coatings, electrical insulation, or structural composites.

Key Features of Curing Agent Resin

Chemical Composition

The chemical makeup of a curing agent is fundamental to the performance of the final epoxy system. Curing agents are typically amines, anhydrides, phenolics, or polyamides that react with the epoxy resin to form a three-dimensional cross-linked polymer network. The specific type and ratio of curing agent used directly influence the physical and chemical properties of the cured material.

For example, aliphatic amines offer fast curing at room temperature and good mechanical strength, while aromatic amines provide superior thermal stability and chemical resistance but require elevated temperatures to cure. Selecting the right chemical composition ensures the epoxy meets requirements for hardness, flexibility, adhesion, and environmental durability.

Curing Mechanism

Epoxy curing agents operate through two primary chemical mechanisms: polyaddition and polycondensation. Polyaddition reactions (common with amine-based hardeners) involve direct addition to epoxy groups without releasing by-products, resulting in high cross-link density and excellent mechanical properties.

In contrast, polycondensation (seen with phenolic or anhydride systems) produces small molecules like water as by-products, which can affect curing in confined environments. The mechanism impacts critical factors such as pot life, exothermic heat generation, and cure speed—all of which must be matched to the application method and working conditions.

Mechanical Properties

The choice of curing agent significantly influences the mechanical behavior of the cured epoxy. Agents that promote dense cross-linking—such as aromatic amines or anhydrides—yield materials with high tensile strength, rigidity, and compressive strength, making them ideal for structural applications in aerospace, automotive, and composite manufacturing.

Conversely, flexible curing agents like polyamides or modified amines reduce brittleness and improve impact resistance, allowing the epoxy to withstand dynamic loads and thermal cycling. This balance between strength and flexibility is crucial when designing materials for demanding engineering environments.

Thermal Resistance

Thermal stability is a critical performance metric, especially in applications exposed to high temperatures. Certain curing agents—such as dicyandiamide, aromatic amines, and novolac resins—enable epoxies to maintain structural integrity at temperatures exceeding 150°C (300°F), and in some cases up to 200°C or higher.

This makes them suitable for use in engine components, electrical insulation systems, and high-temperature adhesives. Thermal resistance also affects the glass transition temperature (Tg) of the epoxy, which defines the upper limit of its useful service temperature.

Chemical Resistance

Epoxy systems are prized for their ability to resist degradation from solvents, acids, alkalis, fuels, and other aggressive chemicals. The curing agent plays a pivotal role in this resistance. For instance, epoxies cured with polyamide or phenolic hardeners exhibit excellent resistance to hydrocarbons and moisture, making them ideal for use in oil refineries, chemical storage tanks, and marine environments.

Dense cross-linking reduces permeability and slows down chemical attack, enhancing the longevity of protective coatings and linings. Proper selection ensures long-term performance in corrosive industrial settings.

Environmental Resistance

Outdoor and marine applications demand resistance to UV radiation, moisture, and thermal cycling. While pure epoxies can degrade under prolonged UV exposure (leading to chalking and yellowing), certain curing agents—particularly aliphatic polyamines and cycloaliphatic amines—improve UV stability and moisture resistance.

These formulations are commonly used in bridge coatings, ship hulls, and exterior construction elements. Additionally, low water absorption rates help prevent delamination and corrosion underneath the coating, ensuring durable protection over time.

Workability and Pot Life

The usability of a two-part epoxy depends heavily on the curing agent’s influence on pot life—the time available for mixing, pouring, brushing, or bonding after the components are combined. Fast-reacting agents like aliphatic amines may offer pot lives as short as 10–30 minutes, suitable for rapid production processes.

Slower-curing agents, such as polyamides or latent hardeners, extend workability to several hours, allowing for large pours, complex molds, or precision bonding tasks. Temperature also affects pot life; higher ambient temperatures accelerate curing, so climate control is essential in sensitive applications.

Feature	Impact on Performance	Common Curing Agents
Chemical Composition	Determines reactivity, flexibility, and compatibility	Aliphatic amines, aromatic amines, polyamides, anhydrides
Curing Mechanism	Affects cure speed, exotherm, and by-product formation	Polyaddition (amines), Polycondensation (phenolics)
Mechanical Strength	Influences rigidity, toughness, and load-bearing capacity	Aromatic amines, anhydrides, novolacs
Thermal Resistance	Enables high-temperature service and dimensional stability	Dicyandiamide, DDS (diaminodiphenyl sulfone)
Chemical Resistance	Protects against solvents, acids, and fuels	Polyamides, phenolic resins
Environmental Durability	Resists UV, moisture, and thermal cycling	Aliphatic amines, cycloaliphatic amines
Pot Life & Workability	Controls application window and processing ease	Modified amines, latent hardeners

Important: Always follow the manufacturer’s recommended mixing ratios and safety guidelines when working with epoxy resins and curing agents. Improper mixing can lead to incomplete curing, reduced performance, or hazardous exothermic reactions. Store curing agents in a cool, dry place away from direct sunlight and incompatible chemicals. Use appropriate personal protective equipment (PPE), including gloves and ventilation, to minimize health risks.

Uses of Epoxy Curing Agent Resin

Epoxy curing agents are essential components in the formulation of epoxy resins, enabling them to transform from liquid to solid through a chemical cross-linking process. These agents not only enhance mechanical strength and thermal stability but also significantly improve chemical and environmental resistance. As a result, cured epoxy systems find widespread application across diverse industries—from heavy-duty industrial manufacturing to creative DIY projects. Their versatility, durability, and performance under extreme conditions make them indispensable in modern engineering and design.

Construction and Automotive Industries

Epoxy resin hardeners are extensively used as structural adhesives in both construction and automotive sectors due to their exceptional bonding strength and resilience. They enable the secure joining of dissimilar materials such as steel, aluminum, glass, concrete, and various plastics—materials commonly found in modern vehicles and buildings.

• In construction, epoxies form high-performance repair mortars, crack fillers, and anchoring systems that endure weather exposure, vibration, and load stress.
• They are used in concrete flooring overlays and structural strengthening with fiber-reinforced polymers (FRP), offering long-term protection against wear and corrosion.
• In automotive manufacturing, epoxy-based adhesives bond body panels, reinforce chassis structures, and replace traditional welding in lightweight designs, improving fuel efficiency and crash safety.
• Auto body shops rely on epoxy repairs for rusted frames, cracked bumpers, and damaged suspension components due to their superior adhesion and fatigue resistance.

Key Benefit: Exceptional load-bearing capacity and resistance to impact and environmental degradation.

Electrical and Electronic Industries

The electrical insulating properties and environmental stability of epoxy curing agents make them ideal for protecting sensitive electronic components. Once cured, epoxies provide a robust barrier against moisture, dust, thermal cycling, and chemical exposure.

• Used in potting and encapsulation processes, epoxies seal circuit boards, transformers, sensors, and connectors, preventing short circuits and mechanical damage.
• They maintain dielectric strength across a wide temperature range (-40°C to +150°C or higher), ensuring consistent performance in harsh environments.
• Epoxies are integral in the production of printed circuit boards (PCBs), where they serve as insulating substrates and protective solder masks.
• High-voltage insulators and switchgear components use epoxy composites for arc resistance and tracking prevention.

Technical Advantage: Long-term reliability and enhanced safety in mission-critical electronic systems.

Aerospace and Marine Applications

In aerospace and marine engineering, weight reduction without compromising strength is paramount. Epoxy curing agents enable the creation of advanced composite materials that meet these demanding requirements.

• In aerospace, epoxies are used with carbon fiber or fiberglass to produce lightweight yet incredibly strong components such as wings, fuselages, tail sections, and interior panels.
• These composites offer excellent fatigue resistance, dimensional stability, and tolerance to extreme temperatures encountered at high altitudes.
• In marine environments, epoxy resins are critical for building and repairing boat hulls, decks, and propellers due to their outstanding resistance to water absorption and salt corrosion.
• They also serve as waterproof barriers in below-waterline coatings and are used in bonding underwater fixtures and fittings.

Performance Edge: High strength-to-weight ratio and long-term durability in aggressive, moisture-rich environments.

Industrial Coatings and Protective Finishes

Epoxy curing agents are the backbone of industrial protective coatings, providing unmatched resistance to abrasion, chemicals, and corrosion. These coatings are applied to metal surfaces in factories, refineries, pipelines, and storage tanks to extend service life and reduce maintenance costs.

• Steel structures exposed to acidic, alkaline, or saline environments are coated with epoxy paints to prevent rust and degradation.
• Flooring systems in warehouses, garages, pharmaceutical labs, and food processing plants use epoxy finishes for seamless, non-porous, and easy-to-clean surfaces.
• Machinery and equipment benefit from epoxy powder coatings that resist chipping, UV degradation, and chemical spills.
• Multi-layer epoxy systems (primer + intermediate + topcoat) are standard in offshore platforms and chemical processing units.

Durability Factor: Long-lasting protection in high-traffic and chemically aggressive industrial settings.

Art and DIY Crafts

Beyond industrial applications, epoxy resin hardeners have gained immense popularity among artists, crafters, and home enthusiasts. Their optical clarity, self-leveling nature, and ability to cure into a glass-like finish make them perfect for creative projects.

• Artisans use epoxy to create jewelry, coasters, river tables, and decorative trays, often embedding pigments, glitter, wood, or dried flowers for visual appeal.
• It’s widely used in mixed media art for sealing and enhancing textures while adding depth and shine.
• Hobbyists apply epoxy for functional repairs—such as fixing ceramics, sealing countertops, or waterproofing outdoor furniture.
• Custom organizers, phone cases, and home décor items are easily made using silicone molds and colored epoxy resins.

Creative Freedom: Enables limitless customization with professional-grade results accessible to beginners.

Emerging and Niche Applications

As technology advances, new applications for epoxy curing agents continue to emerge across innovative fields.

• In renewable energy, epoxies are used in wind turbine blades for their fatigue resistance and structural integrity.
• 3D printing resins often incorporate epoxy chemistry for high-resolution, durable prototypes and end-use parts.
• Dental and medical devices utilize biocompatible epoxies for bonding and encapsulating sensors and implants.
• Sustainable construction uses epoxy-modified concrete to reduce cracking and increase lifespan, minimizing material waste.

Future Outlook: Growing demand in green tech and smart manufacturing is expanding the role of epoxy systems.

Pro Tip: When selecting an epoxy curing agent, consider the required cure time, flexibility, temperature resistance, and compatibility with the base resin. Aliphatic amines offer fast curing at room temperature, while aromatic amines provide higher heat and chemical resistance. For artistic use, opt for UV-stable, low-yellowing formulations to maintain clarity over time.

Industry	Primary Application	Key Properties Utilized	Common Epoxy Type
Construction & Automotive	Structural bonding, repairs, reinforcements	High tensile strength, impact resistance	Bisphenol-A based
Electrical & Electronics	Potting, encapsulation, insulation	Dielectric strength, thermal stability	Cycloaliphatic epoxy
Aerospace & Marine	Composite fabrication, hull repair	Lightweight, moisture resistance	Novolac or phenolic-modified
Industrial Coatings	Flooring, anti-corrosion protection	Chemical resistance, abrasion resistance	Amine-cured bisphenol-F
Arts & Crafts	Decorative casting, sealing, embedding	Clarity, gloss, ease of use	Aliphatic amine-cured

Additional Considerations

• Safety First: Always use gloves, goggles, and ventilation when handling epoxy curing agents—some can cause skin irritation or respiratory issues.
• Cure Time Control: Temperature and humidity affect curing speed; use accelerators or inhibitors as needed for optimal results.
• Surface Preparation: Proper cleaning and sanding ensure maximum adhesion and prevent delamination.
• Environmental Impact: Look for low-VOC or bio-based epoxy systems to reduce ecological footprint.
• Shelf Life: Store curing agents in sealed containers away from moisture and heat to maintain reactivity.

How to Choose the Right Curing Agent for Resin Applications

Selecting the appropriate curing agent for resin plastic is essential for achieving optimal performance, durability, and reliability in any application. The curing agent (also known as a hardener) plays a critical role in determining the final properties of the cured resin, including strength, flexibility, and resistance to environmental factors. This comprehensive guide outlines the key considerations when choosing a curing agent, helping you make informed decisions based on your specific resin type, application requirements, and working conditions.

Important Note: Always verify compatibility between the curing agent and the base resin (e.g., epoxy, polyester, or vinyl ester). Incompatible combinations can lead to incomplete curing, reduced mechanical strength, or premature material failure.

Key Factors in Curing Agent Selection

1. Thermal Resistance

   Applications exposed to high temperatures—such as automotive components, industrial coatings, or aerospace assemblies—require curing agents that enhance thermal stability. Look for agents that promote the formation of highly cross-linked polymer networks, which resist softening, deformation, or degradation at elevated temperatures.

   Common high-temperature curing agents include aromatic amines and anhydrides, which can provide continuous service up to 150–200°C (300–400°F). Avoid aliphatic amines in high-heat environments, as they typically offer lower thermal resistance.

2. Moisture and Chemical Resistance

   For applications in humid, outdoor, or chemically aggressive environments—such as marine coatings, chemical storage tanks, or wastewater treatment systems—choose curing agents that improve the resin’s resistance to water absorption, hydrolysis, and corrosive substances.

   Cycloaliphatic amines and phenalkamines are excellent choices for moisture resistance, while novolac epoxies with appropriate hardeners offer superior protection against acids, solvents, and alkalis. These agents create dense, impermeable matrices that prevent chemical ingress and prolong service life.

3. Curing Time and Temperature

   The curing profile must align with your production process and operational constraints. Fast-curing agents (e.g., aliphatic polyamines) are ideal for rapid turnaround applications, often achieving handling strength within 1–2 hours at room temperature.

   For heat-sensitive substrates (e.g., plastics or electronics), low-temperature curing agents (such as modified amines or catalytic hardeners) allow full cure at temperatures as low as 5–15°C (40–60°F). Conversely, high-performance systems may require elevated temperatures (60–120°C) to achieve maximum cross-linking and mechanical properties.

4. Compatibility with Substrates

   The success of a resin system depends heavily on adhesion to the substrate. Choose a curing agent that enhances bonding to materials like metal, concrete, fiberglass, or composites. For example, amine-based hardeners generally provide excellent adhesion to steel and concrete, while silane-modified agents improve bonding to glass and ceramics.

   Additionally, ensure the curing agent is chemically compatible with the base resin. Epoxy resins, for instance, require amine, anhydride, or catalytic hardeners—using an incompatible agent can result in tacky surfaces or incomplete polymerization.

5. Application Requirements

   The mechanical and physical demands of the end-use application dictate the ideal curing agent. Structural applications—such as load-bearing joints or composite laminates—require hardeners that produce rigid, high-strength networks. Aromatic amines and anhydrides are often used for their superior tensile and compressive strength.

   For flexible coatings, sealants, or impact-resistant materials, opt for curing agents that impart elasticity and toughness, such as polyamides or flexibilized amines. These maintain adhesion under thermal cycling and mechanical stress without cracking or delaminating.

6. Working Conditions

   Environmental factors like ambient temperature, humidity, and ventilation significantly affect curing performance. In high-humidity environments, moisture-tolerant agents (e.g., phenalkamines) prevent amine blush—a waxy surface film caused by reaction with atmospheric CO₂ and moisture.

   In cold climates, use accelerators or low-temperature initiators to ensure proper cure kinetics. Conversely, in hot environments, select agents with extended pot life to prevent premature gelation and allow sufficient working time.

Curing Agent Type	Best For	Temperature Range	Typical Applications
Aliphatic Amines	Fast room-temperature cure, general-purpose bonding	15–30°C (59–86°F)	Coatings, adhesives, electrical encapsulation
Aromatic Amines	High thermal and chemical resistance	80–150°C (176–302°F)	Aerospace, industrial linings, composites
Anhydrides	High-temperature stability, low exotherm	100–200°C (212–392°F)	Electrical insulation, casting, tooling
Polyamides	Flexibility, moisture resistance, ease of use	10–30°C (50–86°F)	Marine coatings, concrete sealers, DIY projects
Phenalkamines	Moisture tolerance, fast cure in damp conditions	5–30°C (41–86°F)	Underground pipelines, marine structures, humid environments

Expert Tip: Always conduct a small-scale test before full application. This allows you to evaluate cure behavior, adhesion, and final properties under actual field conditions. Adjust ratios or switch agents if necessary to optimize performance.

Additional Selection Tips

• Follow manufacturer-recommended mix ratios precisely—deviations can impair curing and reduce performance.
• Consider pot life and working time, especially for large pours or complex molds.
• Use personal protective equipment (PPE) when handling curing agents, particularly amines, which can be skin and respiratory irritants.
• Store curing agents in tightly sealed containers away from moisture and extreme temperatures to maintain shelf life.
• Label all containers clearly and keep safety data sheets (SDS) accessible for handling and emergency procedures.

Choosing the right curing agent is not a one-size-fits-all decision. It requires a careful balance of performance requirements, environmental conditions, and processing constraints. By understanding the chemistry and characteristics of available hardeners, you can significantly enhance the quality, longevity, and reliability of your resin-based projects. When in doubt, consult with resin suppliers or technical experts to ensure optimal formulation for your specific needs.

Frequently Asked Questions About Resin Curing Agents and Hardeners

Q1: What is a curing agent in resin?

A curing agent is a chemical compound added to a resin system to initiate and control the polymerization process, transforming the liquid resin into a solid, durable material. This reaction, known as curing, creates a cross-linked network that gives the final composite its structural integrity and performance characteristics.

Curing agents are essential for thermosetting resins such as epoxy, phenolic, and polyurethane. They often come with accelerators or modifiers that allow technicians to fine-tune the cure time, pot life, and exothermic heat generation based on application requirements—such as casting, coating, or adhesive bonding.

• Epoxy Resins: Typically use amine-based curing agents for room-temperature or elevated-temperature cures.
• Phenolic Resins: Often require acidic catalysts or high heat to complete the cure.
• Polyurethane Resins: React with isocyanate components acting as curing agents to form flexible or rigid foams and coatings.

Proper mixing ratios and environmental conditions (temperature, humidity) are crucial for achieving optimal performance from a curing agent.

Q2: What is the purpose of a resin hardener?

A resin hardener is a specific type of curing agent designed to react with the base resin, triggering a chemical transformation that results in a hardened, stable plastic material. While the terms "hardener" and "curing agent" are often used interchangeably, "hardener" typically refers to the reactive component in two-part epoxy systems.

The selection of a hardener significantly influences the physical and chemical properties of the cured resin, including:

• Mechanical Strength: Tensile, compressive, and impact resistance.
• Flexibility: Some hardeners produce rigid finishes, while others yield flexible, impact-resistant results.
• Chemical Resistance: Resistance to solvents, acids, alkalis, and moisture exposure.
• Temperature Tolerance: Heat deflection temperature and thermal stability.
• Cure Speed: Fast-cure hardeners for quick turnaround vs. slow-cure options for large pours with reduced exotherm.

Manufacturers formulate specific hardeners for different applications—such as marine coatings, industrial flooring, or art casting—to ensure compatibility and peak performance.

Q3: What is a curing agent for epoxy resin?

In epoxy resin systems, the curing agent—commonly referred to as the hardener—is typically an amine-based compound that reacts with the epoxide groups in the resin to form a rigid, three-dimensional polymer network. This reaction is exothermic and proceeds through a process called cross-linking.

Most consumer and industrial epoxy kits (e.g., for countertops, river tables, or coatings) contain aliphatic amine hardeners, which offer good adhesion, clarity, and ease of use at room temperature. However, more demanding applications may require:

• Aromatic Amine Hardeners: Provide superior heat resistance, chemical stability, and durability—ideal for aerospace or high-performance composites.
• Cycloaliphatic Amines: Offer better UV resistance and are often used in outdoor applications.
• Anhydrides: Used in high-temperature curing processes for electrical encapsulation and tooling.

The correct mix ratio (by volume or weight) is critical—deviations can lead to incomplete curing, tacky surfaces, or weakened mechanical properties. Always follow the manufacturer’s instructions for best results.

Q4: What is the difference between a curing agent and a hardener?

While the terms are frequently used interchangeably, especially in epoxy systems, there are nuanced differences in their usage across industries and resin types:

Aspect	Curing Agent	Hardener
Definition	A broad term for any substance that promotes polymerization and cross-linking in thermosetting resins.	A specific type of curing agent, typically used in epoxy systems to denote the reactive second component.
Resin Types	Used with epoxies, phenolics, polyesters, polyurethanes, and silicones.	Most commonly associated with epoxy resins.
Function	Initiates and controls the curing reaction across various polymer systems.	Reacts directly with epoxy groups to form a solid thermoset plastic.
Application Context	Industrial composites, insulation, adhesives, and advanced materials.	DIY projects, coatings, casting, and laminating.
Examples	Methylenedianiline (MDA), phthalic anhydride, peroxides.	Triethylenetetramine (TETA), diethylenetriamine (DETA).

In summary, all hardeners are curing agents, but not all curing agents are called hardeners. The term "hardener" is more colloquial and widely used in consumer markets, whereas "curing agent" is the technically accurate term in materials science and industrial applications.