• Thermal Expansion :

The thermal expansion of most fillers is less than that of PTFE and since the expansion of the composite will be somewhere between that of the two constituents, filled PTFE compounds expand less than unfilled PTFE. During fabrication certain fillers, notably fibers and platelets, become preferentially oriented (as do the particles of PTFE to a much lesser degree). The result is that some compounds have a markedly different expansion in the directions parallel and perpendicular to the direction of moulding.

Thermal expansion is virtually linear below 15°C(59°) a coefficient is quoted; but since there is a transition point at about 19°C(66°F) and the expansion is far from linear above 30°C(86°F) changes in dimension are quoted as a percentage for a given temperature range.

It is very important to note that these figures are actual linear thermal expansions with virtually all stresses removed from the material. Changes in the dimensions of a sped f fed part due to changes in temperature will differ from these figures if stresses are present.

• Thermal Conductivity :

The thermal conductivity of PTFE is very low, making it a good thermal insulating material. Many fillers, notably metals and metal oxides, have high thermal conductivity, but in general they are effectively encapsulated by PTFE so that the conductivity of the compounds is still relatively low.