For many applications the mechanical properties of a product or component are limiting for the function. Parameters such as stiffness, stress and strain are important to understand when designing a product in polymer materials.

Polymer materials exhibit viscoelastic properties, i.e. the mechancial properties varies with load and time in contrast to metals. To understand the viscoelastic properties is important for correct desgin and choice of a polymer for a specifik application which will be subjected to a load. For instance, the result obtained from tensile testing will vary with both time and temperature.