What’s the Best Material for Parts Made with Silicone Molds?

How Do You Choose the Right Material?

Start with Your Part’s Job

Every part has a purpose. Ask yourself:

• Where will it be used? Indoors or outdoors? Hot or cold?
• What forces will it face? Bending, stretching, impact?
• Does it need to look good? Smooth finish? Clear or colored?
• Any safety requirements? Food contact? Skin contact?
• How many do you need? One prototype or 50 parts?

Your answers point to the right material family.

Match Properties to Requirements

Different materials excel at different things:

What Makes ABS a Top Choice?

Strength and Toughness Combined

ABS (Acrylonitrile Butadiene Styrene) is the workhorse of silicone mold materials. It offers a balanced mix of properties that make it useful across many applications.

Key strengths include:

• Impact resistance: Doesn’t crack easily when dropped
• Stiffness: Holds its shape under load
• Dimensional stability: Shrinkage under 0.5% typically
• Surface finish: Takes paint and plating well

Real-world example: A electronics company needed 30 prototype housings for a new tablet. ABS cast in silicone molds produced parts that matched the stiffness of production ABS. Drop tests showed the prototypes survived falls from 1 meter—identical to molded parts.

Where ABS Shines

Perfect applications for ABS parts:

• Consumer electronics: Phone cases, remote controls, device housings
• Toys: Action figures, vehicle bodies, building blocks
• Automotive interior: Trim pieces, bezels, button caps
• Appliances: Control panels, vent covers, handles

Temperature limits: ABS works from -40°C to +80°C. Above 80°C, it softens. Below -40°C, it becomes brittle.

Limitations to Know

ABS isn’t perfect for everything:

• UV sensitivity: Sunlight causes yellowing and brittleness over time
• Chemical sensitivity: Attacked by solvents and some oils
• Not flexible: Bending causes stress whitening or cracking
• Not food-safe: Standard grades not approved for food contact

For outdoor use, add UV stabilizers or plan to paint parts.

Why Choose Polyurethane (PU)?

Flexibility You Can Adjust

Polyurethane stands out because manufacturers can tune its properties. By adjusting the chemical formula, you get materials ranging from soft as rubber to hard as plastic.

The PU spectrum:

• Soft PU (Shore A 30-70): Feels like rubber, bends easily
• Medium PU (Shore A 80-95): Tough but flexible, like tire tread
• Rigid PU (Shore D 50-85): Stiff like ABS or nylon

Real-world example: A footwear company used soft PU in silicone molds to create 50 pairs of custom insoles. The material matched the comfort of production injection-molded PU while allowing design tweaks based on tester feedback.

Where PU Excels

Great applications for PU parts:

• Footwear: Soles, insoles, heel cushions
• Seals and gaskets: Flexible sealing components
• Bumpers and pads: Impact-absorbing parts
• Industrial wheels: Wear-resistant rollers and casters
• Soft-touch surfaces: Grips, handles, overmolds

Wear resistance: PU outperforms most plastics in abrasive environments. Tests show PU lasts 3-5 times longer than ABS in sliding contact applications.

Temperature and Chemical Resistance

PU handles -30°C to +120°C depending on formulation. It resists:

• Oils and fuels (good for automotive)
• Water and moisture (won’t hydrolyze like some plastics)
• Many solvents (check compatibility for specific chemicals)

Limitation: Some PU formulations yellow with UV exposure. Add stabilizers or use aliphatic PU for color stability.

When Should You Use Silicone Rubber?

Extreme Temperature Performance

Silicone rubber laughs at temperatures that destroy other materials. It works from -60°C to +250°C continuously. Short exposures to 300°C are possible.

Why this matters:

• Oven mitts touch hot pans at 200°C+
• Freezer seals stay flexible at -40°C
• Engine gaskets survive under-hood heat
• Medical sterilizations handle autoclave cycles

Medical-Grade Safety

For parts touching the human body, silicone rubber is often the only choice.

Safety credentials:

• ISO 10993 certified for biocompatibility
• FDA approved for food and skin contact
• Hypoallergenic: Causes no allergic reactions
• Non-toxic: Leaches nothing into surrounding tissue

Real-world example: A medical device company needed 100 pacifier prototypes for clinical testing. Silicone rubber cast in silicone molds produced parts that passed all safety tests. The prototypes matched production-grade material properties perfectly.

Where Silicone Rubber Dominates

Best applications include:

• Baby products: Pacifiers, bottle nipples, teething toys
• Medical devices: Catheters, tubing, seals, implants
• Kitchenware: Baking mats, spatulas, microwave gloves
• Electronics: Keypads, gaskets, vibration dampeners
• Automotive: Turbocharger hoses, sensor seals

Unique Properties

Silicone rubber offers capabilities other materials can’t match:

• Transparency: Clear grades available for optical applications
• Colorability: Accepts pigments easily for custom colors
• Release properties: Nothing sticks to silicone surfaces
• Electrical insulation: Excellent dielectric properties
• Compression set resistance: Returns to shape after years of compression

What About Epoxy Resin?

High Rigidity for Structural Parts

Epoxy resin delivers exceptional stiffness and strength. When cured, it forms a rigid, durable material that holds tight tolerances.

Mechanical properties:

• Tensile strength: 40-85 MPa (stronger than most plastics)
• Flexural modulus: 2,000-4,000 MPa (very stiff)
• Compressive strength: 80-120 MPa (handles heavy loads)

Chemical Resistance That Protects

Epoxy stands up to environments that destroy other materials:

• Acids and bases: Resists most chemicals
• Solvents: Unaffected by common cleaners
• Salt water: Perfect for marine applications
• Fuels and oils: Used in automotive and aerospace

Real-world example: A marine equipment manufacturer needed 20 corrosion-resistant sensor housings. Epoxy resin cast in silicone molds produced parts that survived 1,000 hours of salt spray testing with zero degradation.

Where Epoxy Excels

Ideal applications:

• Composite tooling: Master patterns for carbon fiber
• Architectural models: Bridge and building prototypes
• Industrial components: Pump housings, valve bodies
• Electrical insulation: Transformer components, bushings
• Art and jewelry: Cast sculptures, decorative pieces

Bonding and Composite Capabilities

Epoxy’s ability to bond with reinforcements makes it special:

• Fiberglass composites: Epoxy + glass fiber = strong, light parts
• Carbon fiber composites: Epoxy + carbon = aerospace-grade structures
• Filled systems: Add metal powders for metallic appearance
• Core bonding: Attaches to foam or honeycomb cores

How Do Materials Compare Side by Side?

Quick Reference Table

Decision Guide by Application

What Factors Affect Material Choice?

Part Function Drives Selection

Think about what the part does:

• Structural support: ABS, epoxy, rigid PU
• Sealing or cushioning: Silicone, soft PU
• Appearance models: Any material, based on needed finish
• Moving parts: PU for wear resistance, silicone for flexibility

Production Volume Matters

For small batches (1-50 parts): Choose based on properties alone. Cost differences are small.

For medium batches (50-500 parts): Consider mold life. Hard materials like epoxy wear molds faster than soft materials.

Cost per part typically:

• Silicone rubber: $20-50
• PU: $15-40
• ABS: $10-30
• Epoxy: $25-60

Post-Processing Requirements

Some materials need more work after demolding:

What About Specialized Materials?

Transparent Options

Need to see through your part?

• Clear PU: Good optical clarity, yellowing possible over time
• Clear silicone: Excellent clarity, stays clear, more expensive
• Epoxy: Glass-like clarity, yellows with UV

Flame-Retardant Grades

For electronics or aerospace:

• ABS: FR grades available (UL94 V-0)
• PU: Can be formulated with flame retardants
• Epoxy: Inherently flame-retardant with additives

Bio-Based and Sustainable Options

The industry is moving toward greener materials:

• Bio-PU: Made from plant-based sources
• Recycled ABS: Post-industrial and post-consumer content
• Natural rubber: Alternative to silicone for some applications

How Do You Test Material Compatibility?

Small-Sample Testing

Before committing to full production:

1. Make a test mold with a simple shape
2. Cast samples in candidate materials
3. Test properties: Flexibility, strength, appearance
4. Check mold compatibility: Does the material stick? Cure properly?
5. Verify performance: Does it meet your requirements?

Common Issues to Watch For

Inhibition: Some materials prevent silicone curing. Test first.

Shrinkage: All materials shrink. Know the rate for your chosen material.

Sticking: Some materials bond to silicone. Use proper release agent.

Cure time: Different materials need different schedules. Follow data sheets.

How to write a spec that gets priced correctly

A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.

• A master pattern printed or machined to the final finish
• Cast resin grade and the colour you need
• Number of parts required from each mould
• Tolerance on the features that mate
• Finish: as cast, primed or painted

The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.

What actually drives the price

Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:

• master pattern quality
• silicone mould life
• cast material grade
• colour and finish
• number of parts per mould

Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.

Problems you will meet, and the fix

Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.

• Bubbles trapped against a vertical face
• Dimensional drift after the tenth pull from one mould
• Colour mismatch between two moulds
• Shrinkage on a thick section that cools last

Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.

What to check on the first article

The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.

• Every dimension on the drawing, with the measured value written beside it.
• The material certificate, matched to the heat or lot number on the parts.
• The finish against the sample you approved, under the same light.
• Fit against the mating part, assembled rather than measured.
• Packaging, because parts that arrive damaged were never in tolerance.

Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.

How to compare two quotes fairly

Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.

Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.

Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.

Scaling from one part to a batch

The first part teaches you the process. The hundredth teaches you the process cost.

Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.

Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.

What Do Industry Experts Recommend?

Choosing the right part material for silicone molds doesn’t have to be complicated. Each material offers distinct advantages:

• ABS delivers strength and stiffness at moderate cost—perfect for housings and consumer goods
• PU provides adjustable flexibility from soft to rigid—ideal for seals, footwear, and wear applications
• Silicone rubber handles extreme temperatures and meets medical safety standards—the choice for skin contact and harsh environments
• Epoxy resin offers maximum rigidity and chemical resistance—best for structural and industrial parts

The “best” material depends entirely on your specific application. Match material properties to part requirements, test small samples first, and consider the full picture including cost, durability, and post-processing needs.

With the right material in your silicone mold, you’ll produce parts that look good, work well, and stand the test of time.

How we can help

YiguProto runs vacuum casting in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.

Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.

Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our vacuum casting. You can also talk to an engineer before you commit to a drawing.

Frequently asked questions

The short version

Good parts reward the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.

Tighten only what mates. Test a sample before the run. Then let the process do the rest.