The figures below are typical for granular virgin PTFE moulded and sintered to a good standard. They vary with resin, processing and test method, so treat them as orientation and confirm against the datasheet and certificate of the actual material.
| Property | Typical value | What it means in design |
|---|---|---|
| Density | 2.14 to 2.20 g/cm3 | Lower than 2.14 suggests voids or poor sintering. A quick quality check. |
| Melting point (first heat) | about 327 degrees C | Parts are sintered above this, then cooled under control. |
| Continuous service | about minus 200 to plus 260 degrees C | Strength falls steeply with temperature. Use the lower end of capacity when loaded. |
| Tensile strength | 20 to 35 MPa | Low for an engineering plastic. Fillers raise stiffness more than strength. |
| Elongation at break | 200 to 400 percent | Ductile, which also means it deforms under steady load. |
| Hardness | Shore D 50 to 65 | Moderate. Filled grades read higher. |
| Coefficient of friction | 0.04 to 0.10 (against steel) | Among the lowest of any solid. Falls as pressure rises. |
| Linear expansion | about 100 to 125 x 10-6 per K | Allow for it in housings and fits. |
| Dielectric constant | about 2.1 | Stable across frequency and temperature. |
| Water absorption | below 0.01 percent | Dimensionally stable in wet service. |
| Limiting oxygen index | above 95 percent | Does not burn in air. |
Three numbers that catch designers out
Creep. Under a steady compressive stress of a few MPa, virgin PTFE can deform several percent in a day at room temperature, much more when warm. Design on deformation, not on strength.
The room-temperature transition. PTFE crystals change form near 19 degrees C (and a smaller change near 30 degrees C). Volume jumps by about 1 percent over that range, so a part measured on a cold bench is not the size it will be in a warm room. Inspect and machine at a controlled temperature.
Expansion. A 100 mm PTFE ring grows roughly 1 mm when heated by 100 degrees C if free. Constrained in a metal groove, it instead creeps to fill the space and then does not return when cooled, leaving a leak path.
How to use the table
Start with the application load, speed, temperature and fluid. Then ask which of the weak points above are in play. If creep or wear is, move to a filled grade. If elasticity is, add an energiser. If gas permeation matters, check it explicitly.
