Vacuum Casting Silicone: Flexible Parts for Seals, Gaskets & Medical Components
Production-grade silicone vacuum casting for demanding applications. Shore 20A–80A hardness, -50°C to 250°C temperature resistance, and biocompatible medical grades. ISO 9001 certified quality at FIRMFG.
Silicone Vacuum Casting: Flexible Parts for Demanding Applications
Vacuum casting silicone produces flexible, elastomeric parts that rival injection-molded silicone in properties and appearance — without the cost or lead time of steel tooling. Unlike standard polyurethane (PU) casting, silicone vacuum casting delivers genuine silicone rubber parts with exceptional elasticity, temperature resistance from -50°C to 250°C, and biocompatibility for medical and food-contact applications.
At FIRMFG, we cast silicone parts across a Shore hardness range of 20A to 80A using four specialized material grades: medical (USP Class VI), food (FDA compliant), industrial, and electrically conductive. Each mold yields 15–20 copies, making silicone vacuum casting the optimal choice for low-volume production of seals, gaskets, wearable components, and medical devices where true silicone properties are non-negotiable.
This guide covers silicone material grades, the casting process differences from PU casting, design guidelines, cost factors, and applications. Or, skip ahead and request a quote for an immediate price and lead time on your silicone parts.
Silicone Vacuum Casting Specifications
Key capabilities and material properties of silicone vacuum casting at FIRMFG.
| Specification | Value |
|---|---|
| Shore Hardness Range | 20A – 80A |
| Tensile Strength | 4 – 10 MPa |
| Tear Strength | 10 – 30 kN/m |
| Working Temperature | -50°C to 250°C |
| Mold Lifespan | 15 – 20 copies per mold |
| Maximum Part Size | 500 × 350 × 350 mm |
| Dimensional Tolerance | ±0.1 mm (±0.004") |
| Quality Standard | ISO 9001:2015 Certified |
Silicone Material Grades
Four specialized silicone grades cover applications from medical devices to ESD-sensitive electronics. Each grade is tailored with specific mechanical properties and certifications.
Medical Grade
Biocompatible silicone for medical devices, surgical instruments, and implantable components. Meets stringent regulatory standards for patient-contact applications.
| Shore Hardness | Shore 20A – 60A |
| Tensile Strength | 7 – 10 MPa |
| Elongation at Break | 300 – 600% |
| Temperature Range | -50°C to 250°C |
| Certification | USP Class VI, ISO 10993 |
Food Grade
FDA-compliant silicone for food contact applications including bakeware, kitchen utensils, and baby products. Odorless, tasteless, and non-toxic.
| Shore Hardness | Shore 30A – 70A |
| Tensile Strength | 5 – 8 MPa |
| Elongation at Break | 200 – 500% |
| Temperature Range | -40°C to 230°C |
| Certification | FDA 21 CFR 177.2600 |
Industrial Grade
Versatile silicone for seals, gaskets, and industrial components. Excellent compression set resistance and durability for demanding environments.
| Shore Hardness | Shore 40A – 80A |
| Tensile Strength | 4 – 8 MPa |
| Elongation at Break | 150 – 400% |
| Temperature Range | -40°C to 200°C |
| Certification | General purpose |
Conductive Grade
Electrically conductive silicone for ESD protection and electromagnetic shielding. Surface resistance tuned for electronics encapsulation and sensitive component handling.
| Shore Hardness | Shore 50A – 70A |
| Tensile Strength | 4 – 6 MPa |
| Elongation at Break | 100 – 300% |
| Temperature Range | -40°C to 180°C |
| Certification | ESD protection (10⁶ – 10⁹ Ω) |
Casting Process for Silicone: Key Differences from PU Casting
Silicone vacuum casting shares the same basic workflow as PU casting but differs significantly in degassing, curing, mold material, and post-processing requirements.
Vacuum Degassing
Silicone resins have higher viscosity than standard PU resins, requiring extended vacuum degassing of 30–45 minutes (vs. 10–15 minutes for PU). This extended degassing is critical to eliminate trapped air bubbles that would compromise the mechanical integrity and surface quality of the finished parts.
Cure Time
Silicone cure times range from 4 to 24 hours depending on the grade and catalyst system. Addition-cure (platinum) silicones cure faster at elevated temperature (60–80°C), while condensation-cure silicones require longer room-temperature curing. Medical and food grades need full post-curing to achieve biocompatibility.
Mold Material Requirements
A fundamental difference: silicone cannot be cast in a silicone mold because the cast material bonds permanently to the mold surface. Instead, polyurethane molds or specially treated silicone molds with barrier release agents are required. This mold incompatibility is the primary reason silicone casting yields fewer copies per mold.
Post-Curing for Medical & Food Grades
Medical-grade (USP Class VI) and food-grade (FDA) silicone parts require mandatory post-curing at 100–150°C for 2–4 hours. This process drives off residual catalysts and cross-linking byproducts, ensuring full biocompatibility and eliminating any extractable compounds that could leach in service.
Why Silicone Cannot Be Cast in Silicone Molds
The most critical difference between silicone casting and PU casting is mold compatibility. When liquid silicone resin is poured into a silicone mold, the cast material chemically bonds to the mold surface through a phenomenon called silicone-to-silicone adhesion. The part cannot be demolded without destroying both the part and the mold.
To solve this, we use one of two approaches: polyurethane (PU) molds that are chemically incompatible with silicone resin, or specially treated silicone moldscoated with a barrier release agent that prevents bonding. Both approaches reduce mold life compared to standard PU casting, which is why silicone molds yield 15–20 copies instead of the 20–30 typical for PU casting.
Silicone vs Other Flexible Materials
Compare silicone against polyurethane, rubber, and TPU to choose the right material for your application's hardness, temperature, and regulatory requirements.
| Criteria | Silicone | Polyurethane | Rubber | TPU |
|---|---|---|---|---|
| Hardness Range | Shore 20A – 80A | Shore 20A – 90A / 85D | Shore 30A – 90A | Shore 60A – 98A / 70D |
| Temperature Range | -50°C to 250°C | -20°C to 120°C | -30°C to 80°C | -40°C to 120°C |
| Elasticity & Recovery | Excellent | Good | Excellent | Very Good |
| Cost per Part | $30 – $120 | $15 – $80 | $10 – $50 | $20 – $90 |
| Dimensional Precision | ±0.1 mm | ±0.1 mm | ±0.2 mm | ±0.15 mm |
| Biocompatibility | Yes (medical grades) | Limited | No | Limited |
| Mold Life | 15 – 20 copies | 20 – 30 copies | 15 – 25 copies | 20 – 30 copies |
| Wear Resistance | Moderate | Good | Good | Excellent |
Silicone excels in temperature resistance and biocompatibility, making it the only choice for applications above 120°C or requiring medical/food certification. For general-purpose flexible parts below 120°C, PU casting offers better cost-efficiency and longer mold life.
Choose Silicone When
You need temperature resistance above 120°C, biocompatibility for medical or food contact, or true silicone elastomeric properties. Best for seals, gaskets, and wearables.
Choose Polyurethane When
You need 10–100 flexible parts below 120°C with lower cost and longer mold life. PU simulates TPU, rubber, and silicone at 90% material fidelity for most applications.
Choose Injection Molding When
You need 1,000+ silicone parts with exact production material and can wait 4–8 weeks for steel tooling. Best for full-scale production where per-part cost dominates.
Design Guidelines for Silicone Casting
Follow these DFM rules to optimize silicone parts for vacuum casting and reduce mold wear, casting defects, and per-part cost.
| Feature | Recommended | Minimum |
|---|---|---|
| Minimum Wall Thickness | 1.0 mm (0.040") | 0.8 mm (0.031") |
| Draft Angle | 2° – 3° | 1° |
| Shore Hardness Selection | Match production material ±5A | Specify target Shore value |
| Minimum Corner Radius | 0.5 mm (0.020") | 0.3 mm (0.012") |
| Undercuts | Avoid (reduces mold life) | Possible with split mold |
| Engraved/Embossed Text | 0.5 mm depth/height | 0.3 mm depth/height |
| Parting Line Position | Non-cosmetic surface | Concealed by design feature |
| Insert Molding | Supported (metal/plastic inserts) | Pre-place in mold |
DFM Tips for Silicone Casting
- Select Shore hardness based on application: 20A–40A for soft seals and cushions, 50A–70A for general gaskets, 70A–80A for rigid structural parts.
- Avoid sharp corners entirely. Silicone concentrates stress at sharp internal corners, leading to premature tearing. Use a minimum radius of 0.5 mm on all corners.
- Design uniform wall thickness to prevent uneven curing and shrinkage. Variations greater than 20% cause dimensional distortion and internal stress.
- Add draft angles of at least 2° to all vertical walls. Silicone parts grip the mold surface tightly, and insufficient draft causes tearing during demolding.
- Position the parting line on a non-cosmetic surface. The mold split line will be visible as a slight flash on the finished part and requires trimming.
- For multi-material assemblies, design bonding surfaces with mechanical interlocks rather than relying solely on adhesive. Silicone-to-plastic bonds benefit from surface primers.
Surface Finishing Options for Silicone Parts
Silicone parts can be finished with textures, coatings, printing, and bonding to meet cosmetic and functional requirements. Cost varies by finish complexity.
| Finish Type | Description | Cost Index |
|---|---|---|
| Matte Finish | Default texture from untreated silicone mold surface. Non-reflective, natural rubber appearance. | 1.0x |
| Glossy Finish | Achieved by polishing the mold surface before casting. Produces a smooth, shiny appearance on the silicone part. | 1.2x |
| Textured Finish | Custom texture patterns such as leather grain, MT-11010, or geometric patterns applied via textured mold. | 1.3x |
| Silicone Coating | Silicone-compatible primer and topcoat system for custom color matching. Available in Pantone-matched colors. | 1.5x |
| Pad Printing | Logos, text, and graphics printed on flat or gently curved silicone surfaces using silicone-based ink. | 1.2x |
| Bonding & Assembly | Medical-grade adhesive bonding for multi-material assemblies. Silicone-to-plastic and silicone-to-metal bonding available. | 1.4x |
Cost index is relative to unfinished matte silicone parts (1.0x). Actual cost depends on part geometry, surface area, and order quantity. Medical-grade finishes require certified materials and documented processes.
Silicone Coloring & Bonding Notes
- Silicone can be pigmented internally during casting for through-color that will not chip or wear off. Pantone matching is available with a tolerance of ±1 shade.
- Surface coating uses silicone-based paint with a compatible primer. Unlike PU, standard paints do not adhere to silicone without specialized surface activation.
- Silicone-to-silicone bonding uses medical-grade adhesive or self-bonding silicone resin. Design bonding joints with overlap areas of at least 3 mm width.
- Pad printing on silicone requires silicone-based ink and a flame or plasma pre-treatment to achieve adequate ink adhesion and durability.
What Drives Silicone Casting Cost?
Silicone casting costs more than PU casting due to higher material pricing, shorter mold life, and mandatory post-curing for certified grades. Volume discounts apply as mold cost is amortized across more parts.
Silicone Material
$30 – $120 / part
Specialty silicone resin, higher cost than PU due to raw material pricing and lower shot yield
Mold Setup
$200 – $500
PU mold or treated silicone mold required, reusable for 15 – 20 shots
Post-Curing
$10 – $30 / part
Mandatory for medical and food grades; ensures full biocompatibility certification
Surface Finishing
$5 – $40 / part
Coating, pad printing, bonding, and texture application as needed
Cost Example: Same Silicone Part at Different Volumes
| Order Quantity | Unit Cost | Lead Time | Notes |
|---|---|---|---|
| 1 unit (first part) | $480 | 7 – 10 days | Includes master + mold + 1 cast + post-cure |
| 5 units | $125 | 12 days | Mold cost amortized, material cost dominant |
| 15 units | $75 | 18 days | Full mold life, maximum cost efficiency |
Example based on a 100 × 60 × 40 mm Shore 50A medical-grade silicone gasket with matte finish and post-curing. Actual quotes vary with geometry, material grade, and finishing requirements.
Silicone Vacuum Casting FAQ
Answers to the most common questions about silicone vacuum casting at FIRMFG.
QWhat hardness range can silicone vacuum casting achieve?
Cast silicone parts range from Shore 20A (very soft, gel-like) to Shore 80A (firm, hard rubber). This wide range covers applications from soft medical cushions to rigid automotive seals. The hardness is determined by the specific silicone resin grade selected and can be tailored to match your production material specifications within ±5A of the target value.
QCan silicone vacuum cast parts be certified for medical applications?
Yes. Medical-grade silicone resins meet USP Class VI and ISO 10993 biocompatibility standards, making them suitable for medical device components, surgical instruments, and patient-contact applications. These parts require mandatory post-curing at 100–150°C to achieve full biocompatibility and eliminate residual extractables. We provide material certificates and documentation for regulatory submissions.
QWhat temperature resistance do cast silicone parts offer?
Cast silicone parts withstand continuous operating temperatures from -50°C to 250°C, with some grades tolerating brief exposure up to 300°C. This exceptional temperature range makes silicone ideal for automotive under-hood components, kitchen products, and industrial seals. Unlike PU resins that degrade above 120°C, silicone maintains its mechanical properties and elasticity across the full operating range.
QHow many parts can one mold produce for silicone casting?
Silicone casting molds typically yield 15–20 copies, which is slightly lower than PU casting (20–30 copies). This is because silicone cannot be cast directly in a silicone mold — it bonds to the mold surface — so PU molds or specially treated silicone molds with barrier release agents are required. For higher volumes, multiple molds can be produced from the same master pattern to parallelize production.
QHow does the cost of silicone casting compare to PU casting?
Silicone casting costs approximately 50–80% more than PU casting due to higher raw material costs ($30–120 per part vs $15–80) and shorter mold life (15–20 vs 20–30 copies). However, for applications requiring temperature resistance above 120°C, biocompatibility, or true elastomeric properties that PU cannot match, silicone is the only viable vacuum casting option and remains far more economical than injection molding for low volumes.
QWhat is the lead time for silicone vacuum cast parts?
First parts are delivered in 7–10 days, including master pattern creation (1–2 days), mold preparation with PU or treated silicone mold (1–2 days), and casting with post-curing (4–6 days). Medical and food-grade parts require additional post-curing time. Subsequent shots from an existing mold take 1–2 days each. Rush service can deliver first parts in 5 days for non-medical grades.
Applications & Industries for Silicone Casting
Silicone vacuum casting serves industries where flexibility, temperature resistance, and biocompatibility are essential performance requirements.
Medical Seals & Gaskets
Biocompatible seals for medical devices, surgical instruments, and diagnostic equipment
Kitchen Products
Food-grade silicone for bakeware, utensils, and heat-resistant kitchen accessories
Electronics Encapsulation
Protective silicone encapsulation for circuit boards, sensors, and sensitive components
Automotive Seals
Heat-resistant gaskets and seals for engine compartments and lighting systems
Wearable Devices
Skin-contact silicone bands, cushions, and housings for fitness trackers and smartwatches
Baby Products
Food-grade silicone parts for teethers, bottle nipples, and safe baby accessories
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Learn MoreStart Your Silicone Casting Project
Upload your CAD files and get a free silicone casting quote within 24 hours. Our engineers provide DFM feedback, material grade recommendations, and Shore hardness guidance at no cost. ISO 9001 certified quality, tolerances to ±0.1mm, and 7-day turnaround on silicone parts.