Written and maintained by CASRAI Editorial Board
Last updated
General information, not medical advice. This guide describes a material family and how a regulator and standards describe it; it does not recommend a product or a clinical use.
Short answer
Polyethylene (PE) is a plastic made by the catalytic polymerization of ethylene; the US FDA’s food-contact rule defines it in exactly those words. In medical supply work, “polyethylene” is not one material: FDA guidance sorts the ultrahigh molecular weight form used in orthopedic devices into four categories, each tied to a named ASTM standard or processing history.
Definition and scope
Under 21 CFR 177.1520, “polyethylene consists of basic polymers manufactured by the catalytic polymerization of ethylene”. The same section defines polypropylene the same way, from propylene; for another pair of common plastics see polypropylene vs polystyrene.
That rule is a food-contact rule. Its table sets limits for polyethylene by use (articles contacting food, packing or holding food during cooking, and food-contact coatings), such as a density range of 0.85-1.00 and maximum n-hexane extractables of 5.5 percent at 50 C for the first use. It does not name low-density or high-density grades, and it is not a medical-device rule. Read it only as how one regulator defines the polymer.
How polyethylene is made and used in practice
For the ultrahigh molecular weight polyethylene (UHMWPE) used in orthopedic implants, FDA’s guidance Characterization of Ultrahigh Molecular Weight Polyethylene (UHMWPE) Used in Orthopedic Devices (issued April 26, 2019) names two consolidation methods for turning resin into a solid form: compression molding and ram extrusion. It also asks manufacturers to identify the starting resin (for example GUR 1020 or GUR 1050) and the terminal sterilization method, including, for radiation, the type, dose and packaging environment. For how radiation sterilization works generally, see gamma irradiation sterilization.
The guidance is nonbinding: it says it does not establish rights or obligations, and “should” means a suggestion, not a requirement. It applies to class II and class III devices intended for orthopedic applications, including spinal devices, that contain UHMWPE, and it does not cover device-specific functional testing such as wear or impingement.
Types of polyethylene in medical devices
FDA’s guidance describes four general categories of UHMWPE. Every row below comes from that document.
| Category | What the guidance says | Standard named |
|---|---|---|
| Conventional UHMWPE | Made from virgin resin powder; compression molded or ram extruded and not intentionally cross-linked before terminal sterilization | ASTM F648; ASTM F2759 section 5.1 |
| Highly crosslinked (HXLPE) | Extensively radiation-crosslinked, irradiated with more than 40 kGy of gamma or e-beam radiation for improved wear resistance; may also be crosslinked by peroxides, silane or high-temperature exposure | ASTM F2759 section 5.2; ASTM F2565 |
| Antioxidant highly crosslinked (AO-HXLPE) | Highly crosslinked material with an antioxidant such as alpha-tocopherol (vitamin E) blended into the powder or diffused into the consolidated form | ASTM F2695 (powder blended with alpha-tocopherol) |
| Non-conventional | Any other polyethylene, for example lower molecular weight, porous, functionalized (such as hyaluronic acid-modified) or surface-modified | None named |
ASTM F648 is the standard specification for UHMWPE powder and fabricated form for surgical implants; ASTM F2759 is the guide for assessing UHMWPE.
For other everyday plastics in lab consumables, including HDPE and LDPE, see the chemical resistance chart for plastics and which plastics are autoclavable. For measuring plastic density, see ASTM D792.
Where it matters for labs, clinics and supply decisions
The guidance gives a reader a checklist of what a manufacturer is expected to be able to state about a polyethylene material. Use it to read a material specification, not to judge a product.
- Starting resin and consolidation method (ram extrusion or compression molding), recommended for all four categories.
- Terminal sterilization method; for radiation, the type, dose and packaging environment.
- Conventional UHMWPE: tensile properties (yield, ultimate tensile strength, elongation at break), impact resistance (for example Izod) and density, with ASTM F648 Table 2 giving specifications.
- Highly crosslinked: in addition, radiation type and dose, percent crystallinity, melting temperature, trans-vinylene index, oxidation index after accelerated aging, crosslink density, fatigue crack propagation and free radical concentration (usually measured by EPR/ESR, for which the guidance notes there is no standard test method).
Biocompatibility is a separate question; see USP Class VI certification.
Common misunderstandings
- “Polyethylene” is one material. The FDA guidance alone separates four categories with different processing histories and different documentation.
- A food-contact definition governs medical devices. 21 CFR 177.1520 is an indirect food additive rule.
- The FDA guidance is a requirement. It is nonbinding and limited to orthopedic UHMWPE devices.
- Crosslinked and conventional UHMWPE are interchangeable. The guidance treats them as separate categories with additional characterization for crosslinked material.
FAQ
What is polyethylene?
A polymer made by the catalytic polymerization of ethylene, as defined in 21 CFR 177.1520.
What are the types of polyethylene used in medical devices?
For UHMWPE in orthopedic devices, FDA describes conventional, highly crosslinked, antioxidant highly crosslinked and non-conventional categories (table above).
What is the chemical resistance of polyethylene?
Ratings depend on the chemical and grade. See the chemical resistance chart for plastics, which covers HDPE and LDPE.
Are properties the same for every polyethylene?
No. For conventional UHMWPE FDA recommends reporting tensile properties, impact resistance and density, and ASTM F648 Table 2 gives the specifications; other categories add further tests.
Sources
- US FDA, Characterization of Ultrahigh Molecular Weight Polyethylene (UHMWPE) Used in Orthopedic Devices: Guidance for Industry and FDA Staff, April 26, 2019, docket FDA-2016-D-0363. Date checked: 2026-10-30.
- US FDA, 21 CFR 177.1520, Olefin polymers, eCFR current text. Date checked: 2026-10-30.
