Resources
Material Guide
Material choice drives more of your part cost than almost any other decision — it sets wall thickness, cycle time, tool steel, and how much secondary work the part needs. This is a reference to inform your decision, not a recommendation: material selection stays with you.
Injection molding resins
Shrink rates below are typical ranges for unfilled grades — the specific grade's data sheet always governs, and tooling is cut to the shrink of the resin you actually approve. Changing resin family after a tool is cut usually means reworking steel.
| Resin | Typical shrink | Strengths | Watch-outs | Typical applications |
|---|---|---|---|---|
| ABS | 0.004–0.009 in/in | Good impact strength, dimensional stability, easy to paint/plate/pad print | Poor UV and chemical resistance unless modified; not for outdoor exposure unpainted | Enclosures, housings, cosmetic covers, control panels |
| Polypropylene (PP) | 0.010–0.025 in/in | Excellent chemical resistance, fatigue resistance (living hinges), low cost, low density | High shrink and warp risk; low stiffness; poor bonding/painting without treatment | Chemical-contact parts, hinged closures, cases, fluid-handling components |
| Polyethylene (HDPE/LDPE) | 0.015–0.040 in/in | Chemical resistance, impact strength at low temperature, moisture barrier | Very high shrink; low stiffness and heat resistance; difficult to bond | Containers, liners, impact-absorbing components |
| Nylon (PA6 / PA66) | 0.007–0.018 in/in (lower when glass-filled) | High strength and stiffness, wear resistance, good chemical/heat resistance | Absorbs moisture — dimensions and properties shift with humidity; needs thorough drying before molding | Gears, bearings, structural brackets, under-hood parts |
| Glass-Filled Nylon (30% GF) | 0.002–0.006 in/in | Much higher stiffness and dimensional stability than unfilled nylon; low creep | Abrasive — accelerates tool wear (budget hardened steel); fiber orientation causes directional shrink/warp | Load-bearing structural parts replacing metal brackets |
| Polycarbonate (PC) | 0.005–0.007 in/in | Very high impact strength, optical clarity, dimensional stability, heat resistance | Notch-sensitive; poor chemical resistance (stress-cracks with some solvents); requires thorough drying | Impact-resistant guards, lenses, instrument housings |
| PC/ABS Blend | 0.005–0.007 in/in | Balances PC toughness with ABS processability and finish quality; better flow than straight PC | Costlier than ABS; still moisture-sensitive | Enclosures needing impact strength plus a good cosmetic finish |
| Acetal / POM | 0.018–0.025 in/in | Low friction, excellent dimensional stability, fatigue and fuel/chemical resistance | High shrink; poor adhesive bonding; degrades with prolonged heat — avoid long residence times | Gears, bushings, snap-fits, precision mechanical components |
| TPE / TPU | 0.005–0.030 in/in (grade-dependent) | Soft-touch, elastomeric, good for grips and seals; bonds to many rigid substrates in overmolding | Substrate compatibility must be verified before tooling — not all TPE/substrate pairs bond | Overmolded grips, gaskets, seals, vibration dampers |
Die casting alloys
| Alloy | Density | Strengths | Watch-outs | Typical applications |
|---|---|---|---|---|
| A380 Aluminum | ~0.098 lb/in³ | The die casting workhorse: good strength, thermal/electrical conductivity, castability, and corrosion resistance | Porosity risk in thick sections; Wrex runs non-vacuum die casting and does not leak test, so pressure-tight parts are not a fit here | Housings, brackets, heat-dissipating enclosures, EMI shielding |
| A360 Aluminum | ~0.095 lb/in³ | Better corrosion resistance and ductility than A380; good for thinner walls | Slightly harder to cast than A380; typically higher cost | Marine/outdoor exposure parts, thin-wall components |
| Zamak 3 (Zinc) | ~0.24 lb/in³ | Excellent castability and detail, tight as-cast tolerances, superb finish for plating, long die life | ~2.5× the density of aluminum — heavy; lower strength-to-weight ratio | Small detailed hardware, decorative plated parts, precision components |
| Zamak 5 (Zinc) | ~0.24 lb/in³ | Higher strength and hardness than Zamak 3, similar castability | Slightly less ductile than Zamak 3; same weight penalty | Zinc parts needing extra strength or wear resistance |
What we run — and what we don't
We process nearly all thermoplastics, in nearly any color. We do not process thermoset materials, rigid (hard) PVC, or liquid silicone rubber (LSR). On the metal side we run cold chamber die casting in aluminum and zinc alloys. If your part needs a material we don't run, we'll tell you at RFQ rather than take the job and struggle with it.
Color
Plastic parts can be produced in nearly any color, matched to standard color charts. There are three routes, and it's usually a cost decision:
- Blended at Wrex — we mix color concentrate into natural resin in-house. Typically the lowest-cost and most flexible option.
- Pre-colored resin — compounded to your color by a coloring house before it reaches us. Best shot-to-shot consistency, higher material cost, usually a minimum order quantity.
- Standard base resin color — some resins are stocked in several standard colors. If one works, it's the cheapest and fastest route available.
Send a physical color standard whenever appearance matters. Gloss, texture, and resin all change how a color reads — two parts matched to the same chart number in different gloss levels will not look like a match on an assembly.
Four questions that narrow the list fast
- What does it touch? Fuels, solvents, cleaning agents, and skin contact eliminate whole resin families before you look at anything else.
- How hot does it get? Continuous service temperature — not peak — is the number that matters. This is where PP and ABS drop out and PC, nylon, or an alloy step in.
- Does it carry load? If yes, glass-filled grades or die casting usually beat unfilled resin, and you should expect to budget hardened tool steel.
- Does anyone see it? Cosmetic requirements drive gate location, texture, and sometimes the resin itself. Tell us which surfaces are show surfaces before we quote tooling.
Notes on regulated work and compliance documentation
For medical and other regulated components, biocompatibility and any required certifications are the customer's or material supplier's determination for the specific application and contact duration — we mold to the approved grade and maintain lot traceability. Bring the material requirement to the RFQ so it is planned into process controls rather than added afterward. See Medical & Healthcare.
RoHS: certificates can be provided on request — ask at RFQ. REACH: we do not offer or monitor REACH compliance for parts produced at Wrex; that obligation stays with you and your material supplier.
If you need help deciding
We can arrange plastic material analysis through an independent laboratory, and introduce you to a design engineer we have worked with for years for design assistance or reverse engineering. In every case, you remain the party responsible for verifying a material against your product's fit, form, function, assembly, and application. Read the full engineering support scope.
Related
Ready to talk about your project?
Send your drawings or describe your part — an engineer will follow up, not a sales queue.