Machine Injection Wax: Performance, Specifications, and How to Apply It in Industry

Types of Machine Injection Wax

Injection waxes are a diverse group of specialized materials engineered for precision applications across multiple industries. These waxes are designed to be injected into molds using controlled machinery, enabling high accuracy in shape replication, dimensional stability, and ease of removal or melting. From jewelry casting to medical therapy and cosmetic production, each type of injection wax offers unique thermal, mechanical, and chemical properties tailored to specific industrial needs.

Casting Waxes

Engineered for precision in investment (lost-wax) casting, widely used in jewelry and metal fabrication industries.

Advantages

• High dimensional accuracy for intricate designs
• Clean burnout with minimal ash residue
• Excellent mold replication and surface finish
• Compatible with automated injection systems

Limitations

• Sensitive to temperature fluctuations
• Requires precise handling to avoid deformation
• Limited reusability after casting

Best for: Jewelry making, dental prosthetics, aerospace components, fine art sculptures

Therapeutic Waxes

Specially formulated for medical and physical therapy applications, used in wax bath machines for heat therapy.

Advantages

• Controlled melting point for safe skin contact
• Excellent heat retention and even distribution
• Hypoallergenic and non-irritating formulations
• Promotes muscle relaxation and joint pain relief

Limitations

• Not suitable for high-temperature processes
• Limited industrial use outside healthcare
• Requires strict temperature monitoring

Best for: Physical therapy clinics, rehabilitation centers, arthritis treatment, occupational therapy

Modeling Waxes

High-viscosity, elastic waxes ideal for detailed modeling in dentistry and architectural prototyping.

Advantages

• Superior detail retention and edge sharpness
• High elasticity allows for undercuts and complex shapes
• Low shrinkage during cooling
• Easy to carve, file, and modify post-injection

Limitations

• Lower thermal resistance
• More expensive than standard paraffin
• Requires skilled handling for best results

Best for: Dental crowns and bridges, orthodontic models, architectural scale models, sculpting

Paraffin Waxes

A versatile, cost-effective base wax used in cosmetics, packaging, and candle manufacturing.

Advantages

• Widely available and economical
• High melting point (50–70°C) ensures product stability
• Excellent water repellency and barrier properties
• Easily blended with dyes, fragrances, and additives

Limitations

• Can be brittle at low temperatures
• Moderate adhesion to molds
• Derived from petroleum (less eco-friendly)

Best for: Candle production, cosmetic creams, food coatings, paper impregnation

Embedded Waxes

Specialized for embedding patterns in jewelry investment casting, ensuring clean mold creation.

Advantages

• Smooth surface finish enhances final casting clarity
• High flowability for filling intricate molds
• Low ash content ensures clean burnout
• Dimensional stability under injection pressure

Limitations

• Narrow application range
• Requires specialized injection equipment
• Higher cost compared to general-purpose waxes

Best for: Jewelry tree assembly, multi-piece casting, high-volume production runs

Beeswax

Natural, biodegradable wax with skin-friendly properties, ideal for cosmetic and medicinal use.

Advantages

• Renewable and eco-friendly source
• Natural antibacterial and moisturizing properties
• Pleasant aroma and golden hue
• Low melting point (62–64°C) enables gentle processing

Limitations

• Higher cost due to natural sourcing
• Variable composition based on origin
• Less structural rigidity than synthetic waxes

Best for: Organic skincare, lip balms, medicinal ointments, eco-conscious candle making

Type	Melting Point	Primary Use	Eco-Friendliness	Cost Level
Casting Waxes	60–75°C	Jewelry & Metal Casting	Moderate	Medium
Therapeutic Waxes	50–55°C	Physical Therapy	High (skin-safe)	Medium-High
Modeling Waxes	55–65°C	Dental & Architectural Models	Low-Moderate	High
Paraffin Waxes	50–70°C	Cosmetics, Candles, Packaging	Low (petroleum-based)	Low
Embedded Waxes	65–75°C	Jewelry Investment Casting	Moderate	High
Beeswax	62–64°C	Cosmetics, Skincare, Natural Products	Very High	High

Expert Tip: When working with injection waxes, always preheat molds slightly to prevent thermal shock and ensure uniform filling. Use release agents sparingly to avoid surface defects in the final product.

Industrial Applications of Machine Injection Wax

Machine injection wax is a highly versatile material that plays a crucial role across multiple industries due to its precision molding capabilities, thermal stability, and ease of removal. Its ability to replicate intricate details with high fidelity makes it indispensable in manufacturing processes requiring accuracy, repeatability, and fine surface finishes. Below is an in-depth exploration of the key industrial applications where wax injection technology delivers significant value.

Dental Industry

In the dental field, injection wax is essential for fabricating precise models used in restorative treatments. Dentists and lab technicians use it to create detailed wax-ups of crowns, bridges, inlays, onlays, and full or partial dentures. These wax patterns serve as positive models for investment casting, ensuring the final metal or ceramic restoration fits perfectly within the patient’s oral structure.

Additionally, wax is used in bite registration procedures, allowing clinicians to capture the exact occlusal relationship between upper and lower teeth. This ensures proper alignment and function of prosthetic devices. The low viscosity and dimensional stability of dental injection wax enable consistent results, even in complex anatomical configurations.

Jewelry Making

The lost-wax casting (or investment casting) method is foundational in modern jewelry production, and wax injection is at the heart of this process. Artisans and manufacturers inject molten wax into silicone or metal molds to produce highly detailed replicas of original designs. These wax models are then assembled into sprue trees, coated with a ceramic slurry, and fired in a kiln to burn out the wax, leaving behind a hollow mold ready for precious metal casting.

This technique allows jewelers to reproduce intricate filigree, engraving, gemstone settings, and custom textures with remarkable consistency. Automated wax injection systems further enhance productivity by enabling mass production of identical pieces while maintaining artistic integrity and precision down to the micron level.

Automotive and Aerospace

In high-performance engineering sectors like automotive and aerospace, wax injection is integral to the production of complex, high-tolerance components through investment casting. Wax patterns are used to manufacture turbine blades, impellers, exhaust manifolds, engine valves, and structural aerospace fittings—parts that demand exceptional strength, aerodynamic efficiency, and resistance to extreme temperatures.

Hot injection wax is favored for its ability to flow into thin-walled and complex geometries without distortion. After casting, the wax is melted or vaporized cleanly, leaving no residue. This process enables near-net-shape manufacturing, reducing material waste and post-processing requirements. In aerospace applications, this contributes to lighter, more fuel-efficient components with superior performance characteristics.

Prosthetics and Orthotics

The medical prosthetics and orthotics industry relies on wax injection to develop patient-specific devices such as artificial limbs, orthopedic braces, and corrective supports. Using digital scans or physical impressions, technicians create molds into which wax is injected to form accurate, anatomically correct models.

These wax prototypes allow clinicians to assess fit, comfort, and biomechanical alignment before final production in durable materials like carbon fiber, thermoplastics, or metals. The precision of wax injection ensures minimal discrepancies between the prototype and the final device, enhancing patient mobility, reducing pressure points, and improving long-term wearability.

Candle Manufacturing

Wax injection has revolutionized candle production by enabling the creation of consistent, high-quality candles with complex shapes, textures, and internal structures. Unlike traditional pouring methods, injection molding ensures uniform wall thickness, reduces air bubbles, and improves dimensional accuracy—especially important for pillar candles, votives, and decorative sculptures.

Manufacturers can integrate colorants, fragrances, and even embedded elements (like dried flowers or glitter) directly into the wax before injection. Multi-cavity molds increase throughput, making it ideal for commercial-scale operations. Additionally, the rapid cycle times and reusability of molds contribute to cost-efficiency and sustainability in large-volume production.

Cosmetics Industry

In cosmetics, wax injection is employed to formulate and shape products such as lipsticks, balms, eyeliners, and solid perfumes. Precision injection ensures a smooth, air-free fill into metal or plastic tubes and compacts, eliminating cracks and inconsistencies that could affect product performance or appearance.

Waxes like beeswax, carnauba, and candelilla are blended with pigments, oils, and active ingredients, then injected under controlled temperature and pressure to maintain emulsion stability and texture uniformity. This process supports the production of high-end cosmetic products with luxurious feel, consistent release, and extended shelf life. Automated injection lines also ensure hygiene and scalability in cosmetic manufacturing facilities.

Industry	Primary Use of Wax Injection	Key Benefits
Dental	Creating crowns, bridges, dentures, bite registration	High detail accuracy, biocompatible materials, seamless casting prep
Jewelry	Lost-wax casting of intricate metal pieces	Design complexity, repeatability, fine surface finish
Automotive & Aerospace	Investment casting of turbine blades and engine parts	Precision geometry, heat resistance, minimal post-processing
Medical (Prosthetics/Orthotics)	Custom limb and brace modeling	Anatomical accuracy, patient-specific fit, pre-production testing
Candle Making	Shaping decorative and functional candles	Consistent quality, design flexibility, efficient mass production
Cosmetics	Filling lipsticks, balms, solid perfumes	Smooth texture, hygienic processing, uniform product delivery

Note: While wax injection offers numerous advantages across industries, selecting the appropriate wax type (e.g., paraffin, microcrystalline, synthetic, or specialty blends) is critical to success. Factors such as melting point, shrinkage rate, viscosity, and compatibility with mold materials must be carefully evaluated based on the application. Always follow manufacturer guidelines for equipment operation and safety protocols when handling heated wax under pressure.

Key Specifications of Machine Injection Wax

Selecting the right wax for injection molding is crucial for achieving precision, consistency, and efficiency in manufacturing processes. Whether used in candle making, jewelry casting, or industrial prototyping, understanding the technical specifications of injection waxes ensures optimal performance and product quality. Below are the most critical factors buyers and operators should evaluate when choosing wax and configuring injection systems.

Temperature Requirements

Each wax type has a specific melting and operating temperature range that must be carefully controlled during injection. Inconsistent temperatures can lead to incomplete mold filling, warping, or premature solidification.

• Paraffin wax: Melts between 45–68°C (113–154°F), ideal for general-purpose applications like candle making due to its ease of handling and low energy requirements.
• Beeswax: Has a slightly higher melting point of 62–65°C (144–149°F) and offers natural durability and a smooth finish, often used in artisanal or eco-friendly products.
• Synthetic waxes: Engineered for stability, these may have tailored melting points (e.g., microcrystalline wax at 60–90°C) for high-precision applications.

Key insight: Injection machines should feature precise temperature control systems (digital thermostats, PID controllers) to maintain consistent melt viscosity and prevent thermal degradation.

Wax Compatibility with Machines

Not all waxes are suitable for every injection system. Compatibility depends on the machine’s design, pump type, and nozzle configuration.

• High-viscosity waxes (e.g., modeling or investment casting waxes) require robust pumping systems and heated manifolds to prevent clogging.
• Low-viscosity waxes flow easily and are ideal for intricate molds but may require pressure regulation to avoid overfilling.
• Some machines are designed specifically for injection molding applications and may not handle abrasive or fibrous wax blends effectively.

Pro tip: Always verify manufacturer recommendations for wax compatibility to avoid equipment damage and ensure consistent shot accuracy.

Injection Pressure

The required pressure to inject wax depends on its viscosity, mold complexity, and runner system design. Proper pressure ensures complete cavity filling without air pockets or flash.

• Candle production: Typically operates at lower pressures (200–500 psi), sufficient for simple molds and low-viscosity paraffin.
• Jewelry and dental casting: Requires higher pressures (500–1000 psi) to push viscous investment waxes through fine details and long runners.
• Adjustable pressure settings allow operators to optimize flow rates and reduce stress on molds.

Critical factor: Over-pressurization can damage delicate molds, while under-pressurization leads to short shots. Use pressure gauges and trial runs for calibration.

Curing and Solidification Time

After injection, the wax must cool and solidify before demolding. This curing time affects cycle efficiency and production throughput.

• Paraffin wax: May take 30 seconds to several minutes to set, depending on mold thickness and ambient temperature.
• Beeswax: Cools faster due to its narrow melting range and higher thermal conductivity, reducing cycle time in small-batch production.
• Cooling channels or chilled molds can accelerate solidification, especially in high-volume operations.

Efficiency note: Faster curing doesn’t always mean better quality—rapid cooling can cause internal stress or shrinkage in complex geometries.

Machine Customization & Flexibility

Modern wax injection machines vary widely in adaptability. Customizable features enhance versatility across different wax types and product designs.

• Interchangeable nozzles: Allow switching between fine-tip and wide-bore injectors for different mold sizes.
• Digital temperature controllers: Enable precise adjustments and memory settings for different wax formulations.
• Adjustable pressure systems: Support both low- and high-viscosity applications without hardware changes.
• Programmable cycles: Automate injection duration, hold time, and ejection for repeatable results.

Smart investment: Machines with modular designs and software integration offer long-term scalability for evolving production needs.

Application-Specific Considerations

Different industries have unique demands that influence wax and machine selection.

• Jewelry casting: Requires high-detail reproduction and thermally stable waxes that burn out cleanly during investment casting.
• Candle manufacturing: Prioritizes cost-effective materials and fast cycle times with minimal post-processing.
• Prototyping: Benefits from reusable or low-melt waxes that allow rapid iteration and mold testing.
• Medical/dental: Demands biocompatible, precision-grade waxes with tight tolerances.

Expert advice: Match wax properties and machine capabilities directly to end-use requirements for optimal results.

Professional Recommendation: When selecting wax and injection equipment, prioritize consistency and repeatability over raw speed. Invest in machines with real-time monitoring (temperature, pressure, cycle time) and use high-quality, application-specific waxes. Conduct test runs with sample molds to fine-tune settings before full-scale production. For multi-product facilities, choose modular systems that support quick changeovers between wax types and mold configurations.

Wax Type	Melting Point (°C)	Typical Injection Pressure (psi)	Curing Time Range	Common Applications
Paraffin Wax	45–68	200–500	30 sec – 5 min	Candles, packaging, basic molds
Beeswax	62–65	300–600	20–90 sec	Artisanal products, cosmetics, eco-friendly casting
Microcrystalline Wax	60–90	500–1000	1–3 min	Jewelry, dental models, high-detail prototypes
Synthetic/Investment Wax	70–100	600–1200	2–4 min	Industrial casting, aerospace components

Additional Considerations

• Wax Filtration: Clean wax free of contaminants ensures smooth flow and prevents nozzle clogs.
• Thermal Stability: Waxes should resist degradation after prolonged heating in the machine reservoir.
• Shrinkage Rate: Lower shrinkage waxes maintain dimensional accuracy, critical for precision casting.
• Environmental Factors: Consider ventilation and disposal methods, especially when using petroleum-based waxes.
• Machine Maintenance: Regular cleaning of nozzles, seals, and heating elements extends equipment life and ensures consistent performance.

How to Choose Machine Injection Wax: A Comprehensive Buyer's Guide

Selecting the right injection wax is a critical decision that directly impacts the quality, efficiency, and cost-effectiveness of your manufacturing or crafting process. Whether you're involved in investment casting, jewelry making, candle production, or industrial prototyping, understanding the key selection criteria ensures optimal performance and consistency. This guide outlines the most important factors to consider when choosing injection wax and accompanying equipment to help you make an informed, value-driven decision.

Important Note: Using substandard or incompatible wax can lead to defective molds, increased waste, machine clogging, and production delays. Always match the wax properties to your specific application and equipment specifications.

1. Quality: Ensuring Consistent, Flawless Performance

The quality of injection wax is paramount for achieving precision and reliability in your output. High-grade wax ensures clean mold filling, minimal shrinkage, and excellent surface detail reproduction.

• Visual Consistency: Premium wax exhibits uniform color and clarity with no cloudiness, streaks, or discoloration.
• Purity: It should be free from air bubbles, contaminants, or particulate matter that could compromise mold integrity.
• Texture and Homogeneity: The wax must have a smooth, consistent texture throughout—indicating proper formulation and manufacturing control.
• Brand Reliability: Opt for established suppliers with proven track records in industrial or artisanal applications. Reputable brands often provide technical data sheets and batch traceability.

Pro Tip: Conduct a small test run before placing a large order. Evaluate how the wax flows, solidifies, and releases from your molds to verify quality firsthand.

2. Cost: Balancing Budget and Performance

While cost is a major consideration, it should not come at the expense of quality. The total cost of ownership includes not just the wax itself but also the associated equipment and potential waste.

• Wax Pricing Factors: Cost varies based on type (e.g., microcrystalline, paraffin, or specialized casting wax), purity, melting point, and brand reputation.
• Injection Kit and Machine Costs: Injection systems range from manual hand-operated kits to fully automated machines. Advanced models offer temperature control, pressure regulation, and programmable settings for consistent results.
• Long-Term Value: Higher-quality wax may have a higher upfront cost but often reduces rework, waste, and downtime—ultimately saving money over time.
• Bulk Discounts: Many suppliers offer volume pricing, making it cost-effective for high-throughput operations.

3. Supplier Reliability: Building a Trusted Supply Chain

In B2B environments, supplier dependability is crucial for maintaining production schedules and quality standards. A reliable partner ensures consistency and support when issues arise.

• Lead Times: Evaluate average delivery times and responsiveness to orders, especially for urgent needs.
• Minimum Order Quantities (MOQs): Confirm whether the supplier’s MOQ aligns with your production scale—some cater to small artisans, others to large manufacturers.
• After-Sales Support: Look for suppliers who offer technical assistance, troubleshooting help, and warranty coverage on equipment.
• Customer Feedback: Review testimonials, case studies, or third-party ratings to gauge customer satisfaction and problem resolution efficiency.
• Customization Options: Some suppliers can tailor wax formulations to meet specific melting points, viscosity, or ash content requirements.

4. Application: Matching Wax to Your Use Case

The intended application is the most critical factor in wax selection. Different processes demand different wax characteristics.

• Jewelry & Precision Casting: Requires high-detail investment casting wax that melts cleanly without residue and captures fine textures and intricate designs.
• Candle Making: Uses paraffin or soy-based waxes designed for container or pillar candles, often with lower melting points and added dyes or fragrances.
• Industrial Prototyping: May require durable, dimensionally stable waxes that withstand handling and multiple stages of processing.
• Dental Applications: Specialized dental waxes must meet biocompatibility standards and offer precise carving and fitting capabilities.

Did You Know? Some waxes are formulated to burn out completely during the burnout cycle in investment casting, leaving no ash—ideal for high-precision metal casting.

5. Viscosity: Optimizing Flow and Detail Retention

Viscosity determines how easily the wax flows into molds and how well it holds fine details. Selecting the right viscosity is essential for mold fidelity and production efficiency.

• Low-Viscosity Wax: Flows easily into thin channels and complex geometries, making it ideal for highly detailed molds or small features.
• High-Viscosity Wax: Maintains shape better and resists sagging, suitable for larger components or applications requiring structural integrity before curing.
• Temperature Sensitivity: Viscosity changes with temperature—ensure your injection system allows precise temperature control to maintain optimal flow.
• Mold Material Compatibility: Match wax viscosity to your mold material (e.g., silicone, metal) to prevent underfilling or excessive pressure on soft molds.

Selection Factor	Key Considerations	Recommended Actions	Common Mistakes to Avoid
Quality	Color, clarity, bubbles, consistency	Request samples, inspect batch reports	Choosing cheapest option without testing
Cost	Wax price, machine cost, long-term value	Compare total cost of ownership	Overlooking maintenance and waste costs
Supplier Reliability	Lead time, MOQ, support, reviews	Check references, start with small orders	Assuming all suppliers offer same service levels
Application	Jewelry, candles, industrial, dental	Match wax type to end-use requirements	Using general-purpose wax for precision work
Viscosity	Flow rate, detail capture, mold compatibility	Test flow in actual molds	Ignoring temperature effects on viscosity

Final Recommendation: Create a shortlist of 2–3 wax types and suppliers based on your primary application. Run side-by-side tests to evaluate performance, ease of use, and final product quality before committing to a long-term supplier.

Additional Tips for Optimal Results

• Store wax in a cool, dry place away from direct sunlight to prevent premature softening or degradation.
• Regularly clean your injection machine to avoid clogs and ensure consistent pressure and flow.
• Monitor ambient workshop temperature, as it can affect wax behavior during injection and cooling.
• Keep detailed records of wax batches, settings, and outcomes to improve process control over time.
• Consider environmentally friendly or biodegradable waxes if sustainability is a priority for your business.

Choosing the right machine injection wax is more than just a purchasing decision—it's an investment in the quality and efficiency of your entire production workflow. By carefully evaluating quality, cost, supplier reliability, application needs, and viscosity, you can select a solution that delivers consistent, professional results. When in doubt, consult with technical experts or request product demonstrations to ensure compatibility with your equipment and processes.

Frequently Asked Questions About Wax Injection in Dental and Metal Casting

Q1: How does wax injection work in the context of dental prosthetics?

Wax injection is a critical step in the lost-wax casting process used to fabricate precise dental prosthetics such as crowns, bridges, and inlays. In this process, molten dental wax is injected under controlled pressure into a mold to create an accurate wax pattern that mirrors the final restoration.

Once the wax pattern is formed, it is carefully removed and placed into a flask where it is surrounded by a gypsum-based investment material mixed with water. This investment is allowed to set and harden, forming a heat-resistant mold. The entire assembly is then placed in a kiln, where the wax is "burned out" through high heat, leaving a precise cavity in the shape of the original pattern. This cavity is subsequently filled with molten metal or ceramic to create the final prosthetic.

This technique ensures high dimensional accuracy and fine detail reproduction, making it indispensable in modern prosthodontics.

Q2: What are some common mistakes people make when performing wax injections?

Even experienced technicians can encounter issues during wax injection if proper procedures are not followed. Common mistakes include:

• Using incompatible wax: Not all waxes are suitable for every application. Using a wax with incorrect flow properties or melting temperature can lead to incomplete filling or distortion of the pattern.
• Neglecting equipment maintenance: Wax injection machines require regular cleaning and calibration. Residue buildup or pressure inconsistencies can compromise the quality of the wax pattern.
• Using low-quality or damaged molds: Imperfections in the mold—such as cracks, warping, or poor sealing—can result in flash, air bubbles, or misshapen patterns.
• Incorrect preheating: Failing to preheat the mold to the appropriate temperature may cause the wax to cool too quickly, leading to incomplete cavity filling.
• Improper injection pressure or timing: Too much pressure can damage the mold, while too little may result in voids or weak sections in the wax model.

Avoiding these errors requires attention to detail, adherence to manufacturer guidelines, and routine quality checks.

Q3: Which factors determine the success of wax injection in metal casting?

The success of wax injection in both dental and jewelry casting depends on three key interrelated parameters: temperature, pressure, and timing. Mastering these variables ensures consistent, high-fidelity patterns.

Factor	Optimal Range	Impact on Quality
Temperature	60–90°C (varies by wax type)	Ensures proper flow without degradation; prevents premature solidification.
Pressure	1–3 bar (low to medium)	Facilitates complete mold filling while minimizing flash or mold damage.
Timing	2–10 seconds (depending on complexity)	Prevents overflow or underfilling; ensures uniform wall thickness.

Balancing these factors eliminates air entrapment, reduces porosity, and produces smooth, dimensionally stable wax patterns—critical for achieving flawless final castings.

Q4: Is the wax in candle-making similar to the wax used for jewel crafting?

While both candle-making and jewelry crafting involve working with wax, the materials are specifically formulated for their respective applications and are not interchangeable.

• Candle Making: Uses primarily paraffin wax, soy wax, or beeswax—materials chosen for their ability to hold fragrance, burn cleanly, and maintain structural integrity at room temperature. These waxes typically have higher melting points (around 45–65°C) to ensure candles last longer and resist softening in warm environments.
• Jewelry Crafting: Relies on specialized casting waxes, which come in various forms (injection, sheet, or carving wax). These are engineered for precision, with lower melting points (often 50–70°C) and excellent detail reproduction. They are designed to vaporize cleanly during the burnout phase without leaving residue.

In short, although visually similar, the functional requirements of each craft demand distinct wax formulations. Using candle wax in jewelry casting can lead to incomplete burnout, ash residue, and flawed metal castings.

Q5: What is the most commonly used wax for injection molding?

Paraffin wax is the most widely used material in wax injection molding, particularly in industrial and dental applications. Its popularity stems from several advantageous properties:

• Cost-effective: Paraffin wax is inexpensive to produce and readily available globally.
• Excellent flow characteristics: It melts smoothly and flows easily into intricate mold cavities, capturing fine details.
• Controlled melting point: Typically ranging from 50°C to 70°C, paraffin allows for efficient injection and clean burnout.
• Low shrinkage: Minimizes dimensional changes during cooling, contributing to pattern accuracy.
• Compatibility: Works well with a variety of mold materials and investment systems.

While pure paraffin is common, many manufacturers blend it with microcrystalline wax or additives to enhance strength, flexibility, and thermal stability for specialized applications. Despite advances in synthetic waxes, paraffin remains the industry standard due to its reliability and performance-to-cost ratio.