Part design begins with answers to some basic questions about how the part will be used and the environment in which it must operate.

What will be the function of the part?

• Seal a fluid? (Impermeable to particular fluid?)
• Transmit a fluid?
• Transmit energy?
• Absorb energy?
• Provide structural support?

What is the environment in which it will function?

• Water, chemicals or solvents that could cause shrinkage of the part?
• Oxygen or ozone?
• Sunlight?
• Wet/dry situation?
• Constant pressure or pressure cycle?
• Dynamic stress, causing potential deformation

How long must it perform correctly?
What properties must the part exhibit?

• Need to stretch without breaking (high ultimate elongation)?
• Resistance to deformation (high modulus)?
• Resistance to set under extensive load (high compression set)?
• Resistance to dimensional changes or embrittlement in the presence of heat or fluids?