Urethane Casting Services

Urethane casting provides end-use, rigid plastic parts or rubber parts with production-level quality. Built without expensive and time-consuming hard tooling, Xometry’s, one of the leading urethane casting companies, urethane casting process uses a 3D printed master pattern and silicone molds to deliver high-quality, short-run parts up to 30” long. The finished dimensions of urethane cast parts depend on the accuracy of the master model, part geometry, and casting material. In general, a shrinkage rate of + 0.15% is expected.

Cast urethane parts are frequently used when color, surface quality, and toughness are required. Urethane molding is a perfect alternative for insert molding or overmolding in low volumes with diverse material choices. Polyurethane casting can also be used for bridge-tooling between a 3D printed rapid prototype and an injection molding with a balance of quality, cost, and time. Urethane cast parts can also be clear, color-matched, painted (including EMI shielding), have installed inserts, and even custom finished.

Low Volume, Durable Parts with Production-Level Quality

Urethane Casting Materials

Cast urethane parts are often compared to injection molding materials. For example, a stiff urethane cast part may be described as “polycarbonate-like,” and a more flexible plastic may be “polypropylene-like.” We group our urethane materials into general categories to help you make quicker decisions and get the best performance on your project. The list below describes the categories of materials and technical examples when selecting polyurethanes.

Vacuum Casting Polyurethane Resins 

Material Simulation

Strength Shore

Flexion(MPA) TC Max

Product Color Description

Advantage Disadvantage


ABS 83 shD 1790 85 Amber, white and black Good resistance 1
ABS 81 shD 2200 93 Dark Amber Good resistance 1
PS chocs 74 shD 1500 70 White/Black Ideal 1
PP 75-83 shD 600-1300 70 White/Black Good resistance 1
Elastomer 20-90shA / / Milky white/Black Good Blend 1
Elastomer 30-90shA / / Clear Good Blend 1
PC 85 shD 2254 105 White/Black High T℃ 105° 1
PS/ABS 80 shD 2300 120 Black IdealTG 120° 1
ABS 83 shD 1800 85 White 94V0 flame retarding 1
Loaded ABS 87 shD 3300 100 Off White V 0 far 25 1
PMMA 87 shD 2100 100 Clear Coloration TG100° 0.996

Available Finishes for Urethane Casted Parts


Parts have a smooth, satin-like finish due to the master pattern being bead-blasted matte. Clear and translucent parts with this finish will appear frosted. Matte finishes are useful for handheld and high-touch areas as it reduces fingerprint visibility.


A finish that includes some sheen but not high reflectivity. Semi-gloss finishes are in between high-gloss and matte, resulting in a smooth, easy-to-clean surface.


A highly reflective finish is made by polishing the master pattern before making the mold. High-gloss has a high sheen and will have the highest transparency for clear parts. High-gloss is useful for cosmetic models, cleanable surfaces, and lenses.


Xometry can provide additional processing, including custom textures, secondary finishes, painting, and more.

Urethane Color Options

Polyurethanes can be blended with pigments to achieve a variety of colors. Naturally, a urethane may be amber to milky-white in color. Xometry’s clear urethane options are formulated to be colorless. Below are Xometry’s color options:

  • Black
  • Color-Match
  • Natural (unpigmented)
  • Clear (colorless)

Overview: What is Urethane Casting?

The Basics Of Urethane Casting

Urethane casting provides end-use, rigid, flexible, and rubber parts with production-level quality. The urethane casting process uses a 3D-printed master pattern to create a silicone mold that delivers high-quality, short-run parts as an economical alternative to low-volume injection molding.

How Urethane Casting Works

Urethane casting is similar to injection molding in that it requires a tool with a cavity in the shape of the final part. The major difference is that urethane casting uses a “soft” mold made of silicone whereas injection molding using a “hard” metal mold that has been CNC machined. The drawback to urethane casting, then, is that the mold wears out more quickly. However, it is vastly more cost-efficient for low-volume and prototype plastic parts that require production-level quality and surface finishes.

The urethane casting process has 3 major steps:

  1. The Master Pattern: In step one, a master pattern of the final part is made using an additive manufacturing process. Polyjet 3D or stereolithography (SLA) 3D printing processes are most often used due to their ability to produce high-resolution and naturally smooth finish parts. The master pattern is typically hand-finished to achieve optimal surface detail before the creation of the mold tool.
  2. Molding: In step two, the 3D printed master pattern is encased in liquid silicone that cures around the pattern, with the silicone encapsulating all the features of the printed parts. When the mold cures, it is cut into distinct halves and the master pattern or 3D printed part, is removed. This leaves an internal cavity perfectly shaped like the part.
  3. Pouring: In the final step of the urethane casting process, liquid urethane or silicone is poured into the silicone mold, and the mold is then placed in a chamber to help remove air bubbles in the liquid material. For opaque parts, the chamber is typically pressurized. For clear parts, the chamber typically pulls a vacuum to mitigate any bubbles and increase clarity. Once cured, the silicone halves are separated and the newly formed part is removed. This process is repeated until the desired quantity is achieved.

Benefits Of Urethane Casting

Urethane casting has a low-cost and quick turnaround for high-quality plastic parts compared to injection molding or 3D printing. Where injection molding requires an expensive upfront investment for the machining of the mold, the silicone mold required for urethane casting is inexpensive and easy to produce. Additionally, while most 3D printing processes require extensive post-processing to get to a near-finished state, urethane cast parts come out of the mold ready to go. Urethane casting is an excellent choice for creating high-quality prototypes or low-volume production of rigid, flexible, clear, colored, or rubber-like plastic parts.

Urethane Casting Tolerances

Typically Cast Urethane Part Tolerances

Description Tolerance Notes
Distance Dimensions +/- 0.010” or +/- 0.003” per inch, whichever is larger, is typical. Irregular or overly-thick geometries may cause deviances or deflection due to shrinkage.
Shrink Mitigation A shrinkage rate of +0.15% can be expected due to thermal expansion of the liquid, and the response of the flexible mold.
Surface Quality Surface finish is externally smoothed to a satin or matte surface. Grow lines may be present on internal or difficult-to-access features. Polishing or custom finishes must be clearly defined and agreed upon at the point of order.
Feature Definition Sharp corners and text may appear slightly rounded.
Size Recommendation We can offer urethane cast parts as large as 30” (0.762 m) long.
This table is based on the assumption that designs have an adequate draft, radii, and coring for manufacturability. Please see Xometry’s Manufacturing Standards for more information on tolerances per process.

Frequently Asked Questions About Urethane Casting

Why would you choose urethane casting over 3D Printing?

One of the most critical distinctions between urethane casting and 3D printing is material performance and quality. Urethane casting offers higher-performing materials that can better emulate those used in commercial products. In addition, the fit and finish are often better with urethane cast parts. If material performance and appearance are important to you, urethane casting should be a strong consideration.

Why would you choose urethane casting over injection molding?

The primary deciding factor between urethane casting and injection molding is quantity. Urethane casting is an excellent option for very low quantities (e.g., 50 pieces) of production-grade parts. Compared with urethane casting, injection molding will have higher upfront tooling costs that may not justify a low quantity run. Often, our customers use urethane casting as a stepping stone to test and refine their design before they invest in an injection molding tool.

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