Sealing

Plastic seals must have low enough stiffness to conform to mating surfaces and sufficient creep resistance to maintain tight seals. When plastic seals are in contact with moving parts, the plastic must have low enough friction and sufficient wear resistance so that the device can actuate properly throughout many cycles of use.

Additionally, the plastic has to be compatible with the operating temperature of the device and it must withstand any chemicals that it will come into contact with.