Buyers often ask for "PTFE" and receive three very different materials. The wording on the quote matters.
Virgin PTFE
Made from first-use resin with no filler and no recycled content. It is the grade for food contact, pharmaceutical, high-purity chemical and electrical use. Tensile strength and elongation are at their best.
Modified PTFE (often sold as TFM or modified grades)
A small amount of comonomer, typically a perfluoro propyl vinyl ether in the low single-digit percent range, is built into the polymer chain. Compared with standard PTFE the modified grade has:
- smoother, denser structure with fewer voids,
- lower permeation,
- better creep and cold-flow behaviour,
- better weldability,
- a slightly lower crystalline melting behaviour.
It is often the better choice for gaskets, valve seats and seals, and for thin sections where voids matter. It costs more than standard granular PTFE.
Reprocessed PTFE
Machining waste and offcuts of virgin PTFE can be cleaned, ground and moulded again. Properties are lower and more variable than virgin, and traceability to a first-use resin is lost.
Typical uses: mechanical parts where friction and chemical resistance matter but mechanical strength, purity and certification do not. Never specify reprocessed material for food, medical or semiconductor contact.
Recycled or filled fluff
Some low-cost sheet or rod is made from regrind plus filler. If the quote says only "PTFE" and the price is far below others, ask for confirmation of the resin type and a certificate.
How to write it in a specification
State: resin type (virgin, modified, reprocessed), standard (for example ASTM D4894 for granular resins or the moulding standard for the finished shape), filler type and percent by weight, colour or additive restrictions, and certification needs (food, USP, traceability). Add the density and tensile minima you rely on.
Practical test
Weigh and measure a sample to get density. Virgin moulded PTFE reads about 2.14 to 2.20 g/cm3 depending on crystallinity. A lower value signals voids or regrind with filler. This is a screening check, not a certificate.
