The wall thickness of the substrate and overmold should be as uniform as possible to obtain cycle times. Wall thickness in the range from 0.028 to 0.150 in (0.711 to 3.81 mm) will ensure good bonding in most overmolding applications. If the part requires the use of thick sections, they should be cored out to minimize shrinkage problems and to reduce the part weight and cycle time.
Transitions between wall thicknesses should be gradual to reduce flow problems such as back fills and gas traps. The use of radii, 0.020 in (0.508 mm) minimum, in sharp corners helps reduce localized stress. Deep blind pockets or ribs that are difficult to vent should be avoided. Long draws should have a 3-5° draft to help ejection. Properly designed undercuts however are possible with TPE compounds if the part does not have sharp corners and the elastomer is allowed to deflect during ejection.