Vacuum casting materials are usually polyurethane resins designed to copy the properties of common production plastics or rubber. For example, an ABS-like resin can be used to test a product housing, bracket, or latch. However, it is not exactly the same as injection-molded ABS. A successful prototype test only confirms how the part performs under the conditions tested. It does not guarantee that the final production part will perform the same way.
So, instead of asking, “Which resin looks like ABS?” it is better to ask, “Which material will help us test our design?” A resin that works well for a display model may not be suitable for testing a latch that opens and closes many times or a screw boss located near a heat source.
If you are ordering vacuum cast prototypes, start by identifying the exact resin grade. Check its technical datasheet and compare important properties. Then test the finished prototype under real working conditions to make a better decision about your design.
What Are Vacuum Casting Materials?
For plastic-part prototyping, vacuum casting uses liquid polyurethane resin poured into a silicone mold. The mold is made from a master pattern and helps create the required part shape. Vacuum processing removes trapped air and helps produce cleaner parts. The finished part is made from cured resin, not silicone. This process is also known as urethane casting or polyurethane casting.
This difference is important when reviewing a quotation. A “silicone mold” refers to the tool used to make the part, while “rubber-like polyurethane” refers to one type of material used for the finished part. Neither term means the prototype has the same material or performance as the final production part.
Material suppliers offer different types of casting resins, including soft, semi-rigid, rigid, transparent, and special-purpose options. These materials can copy some properties of common production plastics, but their performance depends on the exact resin grade and processing conditions.
MXY’s vacuum casting service offers PU-based resins designed to simulate ABS, PP, and rubber. These materials can be used for visual models and functional prototypes in small batches. Before placing an order, confirm the exact resin grade and its properties to make sure it suits your project.
Which Vacuum Casting Material Family Should You Consider?
Start with the feature you need to evaluate. Then select a candidate resin family and check the grade-level evidence. The following categories are selection starting points, not interchangeable material specifications.
ABS-Like Rigid Polyurethane
ABS-like resins are candidates for product housings, covers and other relatively rigid prototypes. Materialise describes this family as resembling injection-molded ABS and offers grades with different mechanical and thermal properties. It also warns that actual values can vary with casting conditions, geometry and orientation in the mold.
For a housing, prioritize the properties needed for handling, assembly and the particular load case. For a latch, examine deformation and recovery rather than selecting the hardest available resin.
PP-Like or PE-Like Polyurethane
PP-like and PE-like polyurethane grades are intended to approximate selected characteristics of polypropylene or polyethylene. They can be considered for prototypes where greater flexibility or toughness is important. The designation does not establish equivalent hinge life, chemical resistance or behavior under sustained load. Those requirements need separate evidence.
Rubber-Like Polyurethane
Rubber-like resins are candidates for grips, protective features and flexible components. Specify the hardness scale as well as the value: a Shore A designation and a Shore D designation are not interchangeable. Materialise’s rubber-like casting data, for example, identifies hardness using Shore A.
A seal prototype may demonstrate assembly or compression behavior under a defined trial. It does not automatically qualify the final seal material for pressure, chemicals, temperature or long-term use.
Transparent and Special-Purpose Resins
Transparent casting grades can support visual checks through a cover or light-transmitting component. Special-purpose formulations may address higher-temperature or other application requirements. Sika’s portfolio includes both transparent and technical casting systems.
Do not assume that a transparent resin is actual polycarbonate or PMMA. Likewise, flame resistance, food-contact suitability or UV stability must be checked for the exact grade and applicable conditions—not inferred from “ABS-like,” color or appearance. Named grades discussed in this article are reference examples, not confirmation that MXY stocks them.
What Does ABS-Like Actually Mean?
ABS-like means that a casting resin is intended to resemble some characteristics of ABS. It does not mean the part was manufactured from ABS pellets.
ABS is a thermoplastic. The polyurethane systems used in this type of casting cure through a chemical reaction, creating a different material and manufacturing history. Similar appearance or one similar property cannot establish equivalence across impact, temperature, repeated loading or environmental exposure.
Treat appearance, assembly and functional performance as separate approvals. A painted housing can establish an agreed cosmetic reference. The same housing might help check connector clearance. Neither result, by itself, establishes production-material durability.
The strongest approval statement names its scope: “This prototype demonstrated the specified assembly clearance” is more useful than “The material is equivalent to ABS.”
How to Match Material Properties to Your Test
Choose properties according to the intended decision, not according to which datasheet has the most impressive numbers.
For stiffness, examine modulus and geometry. Modulus describes resistance to elastic deformation under the relevant test. A component’s response also depends on its dimensions, ribs, support conditions and load direction. Do not substitute strength for stiffness.
For breakage risk, examine the relevant strength or impact evidence. Tensile strength, flexural strength and impact strength are different measurements. A tensile stress at yield is not automatically the same endpoint as tensile strength.
For flexible features, examine recovery and repeated operation. Elongation at break describes a test specimen at failure; it does not state how often a latch can bend and return to its original position. A part-level trial should measure the behavior that matters to the mechanism.
For heat exposure, examine the method behind the temperature. Heat deflection temperature, or HDT, is measured using a specimen under a specified bending load while temperature increases. ZwickRoell explicitly notes that the result does not establish the maximum operating temperature of the finished product.
For contact with cleaners or fluids, evaluate the exact combination. Identify the agent, concentration, exposure time, temperature and coating state. Missing grade-level evidence is an unresolved requirement, not permission to assume compatibility.
A Real Datasheet Comparison: PX223 HT Versus Terluran GP-22
A comparison between SikaBiresin PX223 HT casting polyurethane and INEOS Styrolution Terluran GP-22 production ABS shows why matching labels, methods and specimen conditions matters. These are published manufacturer values—not results from an experiment performed by MXY.
The Sika sheet checked here is Version 02.01, November 2026. The INEOS ISO datasheet displays the revision string 08/01/2022. Always obtain the current documents for the grades actually proposed for your order.
Flexural Strength: A Qualified Screening Comparison
Sika reports PX223 HT flexural strength of 80 MPa under CQP027-2 / ISO 178. INEOS reports GP-22 flexural strength of 65 MPa at 23°C, also under ISO 178. 7 8
These values describe the same named property with the same named ISO method and units. However, the specimen conditions are not fully matched. Sika links the result to a specified post-cure of 1 hour at 100°C plus 12 hours at 110°C; its current sheet does not state the mechanical-test temperature. That schedule explains the published evidence and is not a universal curing instruction.
The practical conclusion is limited: both grades provide flexural-strength data worth considering. The numbers do not prove that a PX223 HT bracket will outperform a GP-22 bracket or that the materials are interchangeable.
The 2,300 MPa Modulus Trap
Both documents contain a modulus value of 2,300 MPa, but they do not report the same measurement.
Sika lists flexural modulus under ISO 178. INEOS lists tensile modulus under ISO 527. Matching numbers and units therefore do not establish a like-for-like stiffness comparison.
This is a useful procurement check: read the complete row, including the property name and method, before transferring a datasheet value into a material-selection decision.
Impact and Heat Values Need More Context
The current Sika sheet lists an ISO 179 impact result without a complete configuration in the property row. INEOS distinguishes notched and unnotched Charpy results using more specific method designations. These values should not be converted into a simple impact-performance ranking.
The HDT results also refer to different preparation histories: Sika specifies post-curing, while INEOS identifies annealed specimens for its ISO HDT results. Record those conditions rather than presenting the temperature values as equivalent service limits.
Where a critical property lacks a comparable method or specimen condition, request clarification or plan an appropriate test. A missing comparison cannot be repaired by assuming the ABS-like label fills the gap.
Three Functional Prototype Tests and What They Can Prove
The examples below are illustrative test plans, not reported customer results or standardized qualification procedures. Before testing, the responsible engineer should define sample count, loads, duration, environment, measurement method and acceptance criteria. Use suitably equipped personnel or a qualified laboratory where needed.
1. A Loaded Bracket: Deflection and Recovery
Suppose a prototype bracket must hold a small assembly without allowing it to contact a neighboring surface. The question is whether the specified geometry and candidate resin provide sufficient clearance under the intended load.
Mount the bracket using representative supports and fasteners. Measure the initial clearance, apply the defined load at the intended location and record displacement. If the application involves sustained loading, measure displacement over the relevant duration rather than relying on an immediate reading. After unloading, record recovery and any permanent set.
Keep the resin designation, cure history and actual part dimensions with the result. Differences in support stiffness, fastener installation or wall thickness can change the observation.
What a passing result supports: the tested prototype retained the agreed clearance under the recorded setup and exposure.
What remains unproven: production ABS performance, long-term creep beyond the trial, impact resistance and untested temperatures. A short static trial is not a lifetime assessment.
2. A Snap Latch: Repeated Actuation
Suppose a housing latch must open and close repeatedly. Initial assembly fit is only the first question; the team also needs to know whether the latch recovers and continues to engage during the planned evaluation.
Measure initial insertion or release force where relevant, latch engagement and residual gap. Operate the latch against the actual mating feature using a controlled movement. At defined checkpoints, repeat the measurements and inspect the root, engagement surface and surrounding walls for damage or permanent deformation.
Keep temperature, actuation speed and travel consistent. Evaluate the specified coated or uncoated condition; a finish that changes clearance can also change the required movement.
What a passing result supports: the candidate casting and mechanism completed the defined actuation trial within the agreed criteria.
What remains unproven: unlimited cycle life or identical behavior in injection-molded ABS. A failed cast latch can flag a design problem, but the different resin and manufacturing route mean the failure cause must be investigated before rejecting the production design.
3. A Heated Screw Boss: Assembly Stability
Suppose a screw boss sits near a heat-producing component. A resin’s HDT value alone cannot show whether that assembled feature will retain its position and function.
Use representative hardware, mating parts and an installation method accepted for the casting material. Define the mechanical constraint and temperature exposure. Monitor the actual component temperature, not only the chamber setting, and record relevant movement, cracking or retention changes during and after exposure.
The test must reflect whether the real requirement involves a brief temperature rise, sustained heat or repeated cycles. Inspect after cooling as well as during the exposure; recovery can otherwise conceal temporary movement that affected function.
What a passing result supports: the tested assembly met the defined criteria during that thermal and mechanical exposure.
What remains unproven: a universal continuous-use temperature, different fastener installation methods or production-material qualification. Keep the conclusion narrower than the datasheet’s marketing label.
Record Results So They Support a Clear Decision
A result is useful only when another engineer can understand what was tested. Keep the following information together:
- Decision and acceptance criteria: the design question and the limits agreed before testing.
- Part identity: CAD revision, sample identifiers, measured critical dimensions and manufacturing route.
- Material identity: resin designation, datasheet revision and available batch information.
- Delivery condition: cure or post-cure record, time before testing, pigmentation, coating and finishing state.
- Setup and exposure: fixture, hardware, load, duration, temperature and relevant environmental conditions.
- Measurements: initial response, observations during the trial and response after unloading or cooling.
- Disposition: pass, fail or inconclusive for the specified criteria, with photos or supporting records.
- Remaining work: properties, conditions or production-process effects that were not assessed.
A suitable conclusion reads: “The identified samples met the clearance requirement under the recorded bracket test. Long-term behavior and the intended molded ABS part remain unverified.” This is an example of wording, not a reported test outcome.
Avoid turning “no visible damage” into a pass when the requirement concerns displacement, retention or force. If the measurements do not answer the original question, mark the result inconclusive.
When Should You Test the Intended Production Material?
Move to production-material testing when the decision depends on behavior the substitute resin or casting route does not adequately represent. Examples include repeated-use durability, critical thermal loading, chemical exposure or process-sensitive features.
Prototype injection molding can be considered when molded material and processing are central to the evaluation. Confirm the grade and how representative the prototype tooling and molding conditions will be. A trial mold is not automatically identical to the eventual production tool.
CNC-machined plastic prototypes may help with some material-specific checks, but machining does not reproduce injection-molding flow, weld lines or cooling history. Choosing the same polymer family is only one part of making the test representative.
If the casting resin itself is the proposed end-use material, evaluate that identified resin and finished component against the application requirements. It no longer needs to prove equivalence to ABS; it needs to demonstrate suitability for its own intended service.
Choosing Vacuum Casting Materials for Your Next Prototype
Send the supplier the decision you need to make—not only a CAD file and “ABS-like” in the material field. Include the intended production material, critical features, quantity, finish and the loading or exposure your prototypes will encounter.
Request the proposed resin designation, current datasheet and delivery condition. Identify which dimensions apply after painting or other finishing, and state what evidence must accompany the samples. Confirm any test or documentation scope separately; prototype manufacture and dimensional inspection are not the same as laboratory qualification.
MXY’s published vacuum casting capabilities include master-pattern development, silicone tooling, material selection, dimensional inspection and prototype finishing or assembly. Request a vacuum-casting project review with your CAD, target material and evaluation goals so the proposed resin and manufacturing route can be reviewed together.
Frequently Asked Questions
What is the most common material used for vacuum-cast plastic prototypes?
Polyurethane casting resin is commonly used for this type of prototype. Suppliers offer different grades to approximate selected rigid-plastic or rubber-like properties. The right grade depends on the test objective; polyurethane is a material family, not a single specification.
Is ABS-like vacuum-casting resin the same as ABS?
No. ABS-like polyurethane is a casting material selected to resemble some ABS characteristics. It has different chemistry and processing from injection-molded ABS. Use the exact resin designation and relevant test evidence rather than assuming equivalence.
Can ABS-like prototypes be used for functional testing?
Yes, when the resin, geometry and delivery condition are suitable for the defined evaluation. A prototype can support an assembly or load-case decision without qualifying the intended production material for every requirement. Record that boundary in the approval.
Does a higher heat deflection temperature mean a better material?
Not necessarily. HDT describes a particular specimen test under load. It is not the finished component’s maximum operating temperature. Select the material for the actual combination of load, duration, geometry and environment, not the highest temperature number alone.
Can vacuum-cast parts be used as final products?
They can be considered for suitable low-volume applications, but end-use approval must address the exact resin, finished component and service conditions. A prototype’s attractive appearance or successful fit check does not establish regulatory compliance or lifetime durability.
