Does anybody have any design guidelines for this? I have a hand held product that I need to design a protective sleeve for (similar to what you would find on an Ipod/ipad) and I already have a basic design going. The question I have is how much smaller do you make the inside surface of the sleeve so that it has a nice fit when it is stretched over the handheld device. I've never done this before and I would like opinions from people who have done this before I commit to tooling. Thanks.

Josh