VACUUM CASTING / POLYURETHANE

Vacuum Casting Polyurethane: Production-Grade PU Parts

Polyurethane is the most versatile vacuum casting material, simulating ABS, PC, PP, TPU, and transparent plastics. Explore PU grades from Shore 20A to 85D with color matching and production-grade properties at FIRMFG.

Polyurethane Vacuum Casting: Versatile Parts with Production-Grade Properties

Polyurethane (PU) is the most common and versatile material used in vacuum casting. Two-component PU resins can simulate nearly every engineering thermoplastic — from rigid ABS-like and tough PC-like grades to flexible TPU-like elastomers and optically clear transparent resins. This breadth makes polyurethane the default choice for prototyping and low-volume production.

At FIRMFG, our vacuum casting polyurethane service covers a hardness range of Shore 20A to 85D, tensile strengths from 10 to 70 MPa, and heat deflection temperatures up to 120°C. Each silicone mold yields 20–30 parts, delivering production-quality replicas with ±0.1 mm tolerance and 99% surface fidelity in 5–7 days.

This guide details every PU material grade, compares mechanical properties, explains color and finishing options, and breaks down cost drivers to help you select the right resin. Ready to start? Request a quote for an immediate price and material recommendation.

Polyurethane Vacuum Casting Specifications

Key material properties and process parameters for polyurethane vacuum casting at FIRMFG.

Specification	Value
Shore Hardness Range	Shore 20A – 85D
Tensile Strength	10 – 70 MPa
Shrinkage	0.1% – 0.3%
Elongation at Break	5% – 400%
Heat Deflection Temperature	50 – 120°C
Cure Time	2 – 4 hours at 60°C

Polyurethane Material Grades

Five primary PU grades cover the full spectrum of production plastics, from rigid engineering resins to flexible elastomers and optically clear materials.

ABS-like PU

Rigid and impact-resistant, simulating production ABS thermoplastic. Ideal for housings, enclosures, and structural prototypes that require a hard, durable surface.

Hardness: Shore 75D – 85D
Tensile Strength: 45 – 65 MPa
Elongation: 5% – 15%
Impact Strength: 20 – 35 kJ/m²
HDT: 70 – 90°C

PC-like PU

Transparent and tough, replicating polycarbonate properties. Delivers high impact strength and heat resistance for demanding functional prototypes and optical covers.

Hardness: Shore 80D – 85D
Tensile Strength: 55 – 70 MPa
Elongation: 6% – 12%
Impact Strength: 30 – 50 kJ/m²
HDT: 90 – 120°C

PP-like PU

Tough and semi-flexible, mimicking polypropylene. Offers excellent fatigue resistance and living-hinge performance for snap-fit and clip features.

Hardness: Shore 60D – 70D
Tensile Strength: 30 – 45 MPa
Elongation: 50% – 150%
Impact Strength: 15 – 30 kJ/m²
HDT: 60 – 80°C

TPU-like PU

Elastomeric and flexible, simulating thermoplastic polyurethane. Used for gaskets, seals, overmolded grips, and soft-touch components that require repeated flexing.

Hardness: Shore 60A – 90A
Tensile Strength: 10 – 25 MPa
Elongation: 200% – 400%
Impact Strength: No break
HDT: 50 – 70°C

Transparent PU

Optically clear, producing glass-like parts with light transmission above 90%. Suited for lenses, display windows, and light guides where clarity is critical.

Hardness: Shore 70D – 85D
Tensile Strength: 50 – 65 MPa
Elongation: 5% – 10%
Impact Strength: 20 – 40 kJ/m²
HDT: 80 – 110°C

PU Material Properties Comparison

Comprehensive mechanical properties for all five polyurethane grades, measured per ASTM and ISO standards on cured specimens.

Grade	Density	Hardness	Tensile Strength	Flexural Strength	Impact Strength	Elongation	HDT
ABS-like	1.05 – 1.15 g/cm³	75D – 85D	45 – 65 MPa	60 – 90 MPa	20 – 35 kJ/m²	5% – 15%	70 – 90°C
PC-like	1.10 – 1.20 g/cm³	80D – 85D	55 – 70 MPa	80 – 110 MPa	30 – 50 kJ/m²	6% – 12%	90 – 120°C
PP-like	0.95 – 1.05 g/cm³	60D – 70D	30 – 45 MPa	40 – 60 MPa	15 – 30 kJ/m²	50% – 150%	60 – 80°C
TPU-like	1.05 – 1.20 g/cm³	60A – 90A	10 – 25 MPa	N/A (flexible)	No break	200% – 400%	50 – 70°C
Transparent	1.10 – 1.18 g/cm³	70D – 85D	50 – 65 MPa	70 – 100 MPa	20 – 40 kJ/m²	5% – 10%	80 – 110°C

Values represent typical ranges for fully cured specimens. Actual properties vary with resin brand, cure profile, and part geometry. Data sheets are available on request.

Color Matching & Surface Finishing

Polyurethane cast parts can be color-matched, textured, and decorated to closely replicate injection-molded production parts for prototypes and display samples.

Pantone Color Matching

Pigment is mixed into the PU resin before casting for solid, through-color parts matched to Pantone, RAL, or custom references. Color runs throughout the material, so scratches do not reveal a different substrate.

Surface Textures

Smooth, matte, and leather-grain textures are replicated directly from the master pattern. The silicone mold captures surface detail at 99% fidelity, transferring texture to every cast part without additional processing.

Painting & Printing

Spray painting applies opaque RAL or Pantone topcoats, while pad printing adds logos, text, and graphics on flat surfaces. Soft-touch paints and metallic finishes are available for premium cosmetic samples.

Finishing Options & Cost Index

Finishing Option	Description	Cost Index
Pantone Color Matching	Pigment added to resin before casting for solid, throughout color	1.0×
Smooth Surface	Polished master pattern, Ra 0.8 μm finish on cast parts	1.0×
Matte Texture	Sandblast or texture on master, replicates as satin finish	1.1×
Leather Grain Texture	Textured master replicates leather grain on cast PU parts	1.3×
Spray Painting	Topcoat painting in any RAL or Pantone shade for opaque parts	1.5×
Pad Printing	Flat-surface pad printing for logos, text, and graphics	1.6×

Cost index is relative to a baseline cast part with through-color and smooth finish. Multiple finishing options can be combined on a single part.

The Casting Process for Polyurethane

PU vacuum casting follows five controlled steps from resin mixing to post-cure, ensuring consistent mechanical properties and bubble-free parts every shot.

5 min

Step 1: Resin Mixing

Two-component polyurethane resin (Part A + Part B) is measured by weight or volume at ratios ranging from 1:1 to 100:100, depending on the grade. Precise metering ensures consistent hardness and mechanical properties across every cast part.

Typical use: Programmable mixing system for ratios 1:1 to 100:100

5 – 15 min

Step 2: Vacuum Degassing

The mixed resin is placed in a vacuum chamber to remove entrapped air bubbles. Degassing lasts 5–15 minutes depending on viscosity and pot life. Thorough degassing is essential for bubble-free parts, especially for transparent and high-gloss finishes.

Typical use: 5 – 15 min degassing, vacuum below 1 mbar

3 – 5 min

Step 3: Vacuum Casting

Degassed resin is poured into the silicone mold cavity inside the vacuum chamber. Vacuum-assisted filling ensures complete reproduction of fine details, thin walls, and complex geometries without trapped air or incomplete fill.

Typical use: Vacuum-assisted pour, fill time 1 – 3 min

2 – 4 hours

Step 4: Heat Curing

The filled mold is transferred to a curing oven at 60°C for 2–4 hours. Heat accelerates the cross-linking reaction, achieving full mechanical properties and dimensional stability. Cure time varies with resin grade and part thickness.

Typical use: Oven cure at 60°C, 2 – 4 hours per shot

2 – 4 hours

Step 5: Post-Cure (Engineering Grades)

High-performance grades such as PC-like and high-temperature PU require a secondary post-cure at 80–120°C for 2–4 hours. Post-curing maximizes heat deflection temperature, impact strength, and chemical resistance for demanding applications.

Typical use: Post-cure at 80 – 120°C for engineering grades

Design Guidelines for PU Cast Parts

Follow these DFM rules to optimize polyurethane parts for vacuum casting, minimizing defects and extending silicone mold life.

Feature	Recommended	Minimum
Minimum Wall Thickness	1.2 mm (0.047")	0.8 mm (0.031")
Draft Angle	2°	1°
Maximum Wall Thickness	3 mm (0.118")	5 mm (0.197")
Wall Uniformity	Uniform ±20%	Avoid abrupt transitions
Insert Molding	Supported (metal inserts)	Pre-place in mold
Engraved/Embossed Text	0.5 mm depth/height	0.3 mm depth/height

DFM Tips for PU Vacuum Casting

Keep wall thickness uniform and below 5mm. Thick sections cure unevenly, trap heat, and may shrink or crack during demolding.
Add draft angles of 1–2° to all vertical walls to prevent tearing the silicone mold during demolding and extend mold life.
Support metal inserts for insert molding by pre-placing them in the mold cavity before casting, ensuring secure encapsulation.
Specify embossed or engraved text at 0.3mm minimum depth to ensure legibility after casting and finishing.
Position the casting gate on a non-cosmetic surface, as the gate leaves a small mark that requires trimming after demolding.
Specify the PU grade and Shore hardness on drawings. Resin selection drives mechanical performance, cost, and lead time.

What Drives Polyurethane Casting Cost?

The total cost of PU vacuum casting combines a one-time mold setup with per-part material, curing, and finishing. Volume discounts apply as mold cost is amortized.

PU Resin Material

$15 – $80 / part

Varies with part size, grade, and Shore hardness

Silicone Mold

$150 – $500

One-time setup, reusable for 20 – 30 shots

Finishing & Painting

$5 – $30 / part

Color matching, textures, pad printing

Post-Cure & QC

$2 – $10 / part

Engineering-grade post-cure and inspection

Cost Example: Same Part at Different Volumes

Order Quantity	Unit Cost	Lead Time	Notes
1 unit (first part)	$650	7 days	Includes master + mold + 1 cast
5 units	$130	10 days	Mold cost amortized, per-part dominant
10 units	$80	12 days	Approaching optimal batch efficiency
20 units	$55	15 days	Full mold life, maximum efficiency
30 units	$48	18 days	Second mold required for continuation

Example based on a 100 × 60 × 40 mm ABS-like part with through-color and matte finish. Actual quotes vary with geometry, PU grade, and finishing requirements.

Polyurethane Vacuum Casting FAQ

Answers to the most common questions about polyurethane vacuum casting at FIRMFG.

QWhat is the hardness range of polyurethane vacuum casting?

Polyurethane vacuum casting resins span a hardness range from Shore 20A (soft, rubber-like) to Shore 85D (hard, rigid plastic). Soft TPU-like grades fall between Shore 60A and 90A, while rigid ABS-like, PC-like, and transparent grades range from Shore 60D to 85D. This broad range lets one process replicate everything from elastomeric seals to hard structural enclosures.

QCan polyurethane cast parts be color matched?

Yes. PU resin accepts pigment throughout the material for solid, through-color parts matched to Pantone or RAL references. For multi-color or opaque finishes, spray painting and pad printing are applied after casting. Texture and color can be combined — for example, a matte leather-grain surface in a custom Pantone shade — to closely replicate production molded parts.

QCan vacuum casting produce transparent polyurethane parts?

Yes. Transparent PU grades produce optically clear parts with light transmission above 90%, simulating polycarbonate and PMMA. Pressure casting in a pressure pot at 4 bar eliminates micro-bubbles for maximum clarity. Transparent parts can be tinted, smoked, or left fully clear, and post-curing enhances optical stability and surface hardness.

QWhat temperature resistance do polyurethane cast parts have?

Heat deflection temperatures range from 50°C for flexible TPU-like grades up to 120°C for PC-like and high-temperature PU grades. Standard ABS-like parts withstand around 70–90°C. Engineering grades that require post-curing at 80–120°C achieve the highest thermal stability, making them suitable for housings exposed to warm environments and functional testing under heat.

QAre food-grade or FDA-compliant polyurethane resins available?

A limited selection of polyurethane resins is formulated for food-contact and skin-contact applications, compliant with FDA or EU 10/2011 standards. These are typically rigid, neutral-colored grades used for packaging prototypes and consumer product housings. Because vacuum casting uses silicone molds, certified food-grade parts are best suited for prototyping rather than serial food-contact production.

QHow does polyurethane vacuum casting cost compare to other materials?

PU vacuum casting sits between 3D printing and injection molding on cost. Per-part PU material runs $15–$80 depending on size and grade, with a one-time mold cost of $150–$500. At volumes of 1–30 parts it is far cheaper than injection molding (which needs $5,000–$50,000 tooling) and delivers better surface finish and material fidelity than 3D printing. Above 500 parts, injection molding becomes more economical.

Applications for Polyurethane Cast Parts

PU vacuum casting serves applications where production-grade material properties, cosmetic finish, and fast turnaround are required at low to medium volumes.

Enclosure Parts

Electronic housings, remote controls, device covers

Handles & Grips

Soft-touch overmolded grips, tool handles

Buttons

Keypads, membrane switches, tactile controls

Seals & Gaskets

Flexible TPU-like seals, O-rings, weather stripping

Display Samples

Marketing models, sales samples, trade show demos

Wearable Devices

Smartwatch cases, fitness tracker housings

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Start Your Polyurethane Casting Project

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