Resin Data
TPO
Poliolefina Termoplástica
TPO·Thermoplastic Elastomers·Amorphous
TPO (Thermoplastic Polyolefin) is the world's #1 material for automotive bumpers, fascias, and exterior body panels —every time you see a painted plastic bumper on a modern car, it's almost certainly TPO. It's a physical blend of polypropylene (PP) as matrix + ethylene-propylene elastomer (EPDM, EPR or POE) as dispersed phase, without vulcanization (that distinguishes it from TPV which is dynamically vulcanized). The result is a material with PP's processability but excellent impact even at -40°C, paintability, and UV/weather resistance that no PP alone matches.
Global brands: LyondellBasell Hifax (world automotive leader, CA 387 A grades for painted fascias, TKC 805P with talc), Mitsui Tafmer, Asahi Kasei, Borealis Daplen. Very low density (0.88-0.95 g/cm³), high MFI, little to no drying needed —processing very similar to conventional PP.
Important: "TPO" has two completely distinct worlds: injection TPO (this article —bumpers, dashboards, interiors), and TPO roofing membranes (sheet/film for commercial roofs —GAF EverGuard, Carlisle Sure-Weld, Johns Manville, ~40% of USA commercial roof market). They share basic chemical composition but are entirely different industries and processes. Are you running TPO in automotive? Share your experience with paint adhesion and warpage in the comments.
The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.
This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.
These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.
General Properties
| Chemical Structure | Amorphous |
| Specific Gravity (Density) | 0.97:1 |
| L/D Ratio | 18 – 24 |
| Compression Ratio | 2.5 – 3.5 |
| Tonnage Factor | 3.86 – 5.41kN/cm² |
| Thermal Diffusivity | 0.1473mm²/s |
| Max Shear Rate | 20,0001/s |
| Shrinkage | 0.8 – 1% |
| Regrind | 30% |
| Heat Deflection (HDT) @ 1.82 MPa | 45°C |
| Glass Transition (Tg) @ 10°C/min | -65°C |
| Vicat Softening @ 50N | 42°C |
Drying
| Drying Temperature | 82 – 99°C |
| Drying Time | 1 – 2h |
| Recommended Moisture | 0.05% |
| Recommended Dryer Type | Desiccant |
| Dew Point | -40°C |
Temperatures
| Melt | 204 – 232°C |
| Nozzle | 216 – 227°C |
| Front | 210 – 221°C |
| Middle | 204 – 216°C |
| Rear | 193 – 210°C |
| Demolding | 27 – 71°C |
| Mold (Cooling) | 10 – 60°C |
| Feed Throat | 35 – 79°C |
Processing
| Back Pressure | 3.4 – 6.9bar |
| Screw Speed | 50 – 100RPM |
| Injection Speed | Medium |
| Barrel Occupancy | 25 – 75% |
| Injection Pressure | 150 – 800Pbar |
| Holding Pressure | 38 – 640Pbar |
| Cushion | 5.1 – 12.7mm |
Mold
| Runner Diameter | 4.06 – 7.11mm |
| Gate Diameter | 1.02 – 1.52mm |
| Gate Area | 0.81 – 1.82mm² |
| Wall Thickness | 0.76 – 5.08mm |
Venting
| Depth (Vent Depth) | 0.0102 – 0.0203mm |
| Land (Vent Land) | 0.762 – 1.52mm |
| Width (Vent / Clearance) | 4.06 – 10.2mm |
| Relief (Relief Channel) | 0.2032 – 0.4064mm |
Frequently asked questions
A **TPO** (Thermoplastic Polyolefin) is a **heterophasic blend** of:
- **Polypropylene (PP)** as **"sea" matrix** (~50-80% by weight) —provides rigidity, temperature, processability, chemical resistance.
- **Ethylene-propylene elastomer** (EPDM, EPR or POE — polyolefin elastomer) as **dispersed "islands"** at micron scale (~20-50% by weight) —absorb impact, provide flexibility, improve low-temp performance.
**Difference vs regular PP**:
- PP impact copolymer (with in-reactor polymerized ethylene) has ~5-15% ethylene → moderate impact.
- TPO (mechanical blend of PP + added EPDM) has 20-50% elastomer → **much higher impact**, low-temp toughness, superior paintability.
Five combined reasons no other material matches at the same cost:
- **(1) Low-temperature impact**: EPDM maintains toughness at -40°C —critical for bumpers in cold climates (Canada, northern EU, alpine).
- **(2) Low density** (~0.95 g/cm³): lightweight, fuel efficiency.
- **(3) Superior paintability** with adequate primer: Hifax CA grades receive automotive line base-coat/clear-coat paint without difficult pre-treatment.
- **(4) UV and weather resistance** with added HALS stabilizers: 10+ years of outdoor exposure without visible degradation.
- **(5) Low cost**: ~$2-4/kg vs $3-6 for equivalent TPV —important in large components like a 5-8 kg bumper.
Standard OEMs: Toyota, VW, GM, Ford, Hyundai use TPO in virtually all passenger bumpers since the 2000s.
- **Drying**: **typically not required** —it's polyolefin, non-hygroscopic. Some grades with masterbatch or special pigments benefit from 1-2h at 80°C.
- **Melt**: **200-240°C** (typical Hifax: 220°C; with talc/reinforcement: 230-250°C).
- **Mold**: **30-60°C** —relatively cold like other polyolefins.
- **Injection speed**: high —extreme shear thinning, good filling of long thin walls (3-4 mm in 1.5 m bumpers).
- **Residence**: <10 min. PP is stable, but EPDM can degrade if sustained >270°C.
It's one of the easiest TPEs to process —any machine designed for PP processes TPO without modifications.
- **TPO**: mechanical PP + EPDM blend **without vulcanization**. The elastomer is dispersed but **not crosslinked**. Result: more rigid, easy processability, **better paintability** and dimensional stability, **lower compression set** (doesn't recover as well after permanent deformation). Application: bumpers, semi-rigid exterior parts.
- **TPV** ([Thermoplastic Vulcanizate](/en/desktop/datos-de-resina/tpv)): PP + EPDM blend with EPDM **dynamically vulcanized** during mixing. Result: **much better compression set** (15-30% vs TPO's 60-80%), **better thermal and chemical resistance**, more "rubbery" behavior. Application: seals, hoses, parts subject to cyclic deformation.
**Rule of thumb**: bumper/fascia/painted exterior → **TPO**. Seal/gasket/hose → **TPV**.
**They have similar chemical basis (PP + EPDM/POE) but are entirely different industries**:
- **Injection automotive TPO**: pellets in bag, injected in machine, makes bumpers, dashboards. Brands: Hifax (LyondellBasell), Tafmer (Mitsui).
- **TPO membrane roofing**: 1.2-2.0 mm thick sheet, manufactured by extrusion + calendering or coating, with reinforced polyester backing, sold in rolls for flat commercial roofs. Brands: GAF EverGuard, Carlisle Sure-Weld, Johns Manville, Elevate (Holcim, ex-Firestone).
They occupy **~40% of USA commercial roofing market** (vs EPDM and PVC). Welded by hot air on the roof, forming a monolithic membrane resistant to UV, hail, ponding water, fire (Class A) for 20-30 years.
**1.0-2.0% in natural grades without talc**, **0.7-1.3% with 20% talc**, **0.5-1.0% with 33% talc** (Hifax TKC 805P). TPO shrinks less than pure PP because the elastomeric component dampens PP crystallization. Anisotropy is moderate —MD and TD typically differ 0.1-0.3%. For 1.5 m long bumpers, a 0.8% shrinkage represents **12 mm** —oversized design mandatory and machine validation before closing the mold.
**Yes, with adequate primer**. Standard process:
- **Plasma or flame treatment** of TPO surface to increase **surface tension** from ~30 dyn/cm to ~45+ dyn/cm —untreated TPO has low surface energy and doesn't receive paint adequately.
- **Chlorinated or aqueous adhesive primer** specialized for polyolefins (PPG, BASF, Axalta have TPO primers).
- **Base-coat + clear-coat** on robotic OEM paint shop line —passes oven cycle (~120-140°C) without deformation.
Specific Hifax CA painting grades have optimized formulation (low surface defect, paint flow control). Once painted, durability is 10+ years outdoor without chipping or peeling.
Beyond **bumpers/dashboards** (its world's #1 use), TPO is used in:
- **Flexible cable insulation**.
- **Low-cost footwear** (sandals soles, non-premium flip-flops).
- **Household appliances** (internal housings, ducts).
- **Interior construction** (flexible profiles, non-critical seals).
- **Soft toys** (alternative to PVC with phthalates).
- **Sports equipment** (backpack panels, protectors).
In all these cases it competes with **TPE-S (SBC)** which has better soft-touch but less chemical resistance and similar cost.
**Yes, excellent recyclability** —it's one of the easiest TPEs to recycle mechanically. **Up to 50% regrind** in industrial grades without significant loss. **It's thermally stable**, withstands multiple extruder passes. OEM **bumper recycling programs** (Renault, Toyota, GM) recover bumpers from end-of-life vehicles, grind them, separate paint with mechanical/chemical treatment, and reincorporate into the loop —a new bumper can contain **30-50% recycled TPO** without technical issues.
It's **less hygroscopic** and **halogen-free** than PVC, making it a favorite for OEMs committed to circular economy (VW Group, Volvo, Renault Eco-Plastic programs).
**Warpage in large thin parts**. 1.5 m × 0.5 m × 3 mm thick TPO bumpers are especially susceptible to warping if:
- **Gate location** doesn't balance flow well (generates crystallization differential).
- **Mold cooling** isn't uniform (hot zones generate more crystallinity and more shrinkage).
- **Packing pressure** is insufficient (elastomeric material doesn't compensate PP shrinkage).
**Cure**:
- Balanced multiple gate design (cold runner with drops, or hot runner with multi-tip).
- Conformal cooling channels as close as possible to the cavity.
- Stepped packing profile with high holding pressure in critical zones.
- For talc/mineral grades: MD-oriented fiber/mineral reduces transverse warpage —but flow path must be designed so orientation falls where convenient.
Second issue: **inconsistent paint adhesion** without adequate surface treatment —discussed in FAQ #7.