What to use for shockproof/durable "rubber bumper strip

I am making a model for a product I am working on in class…It needs to be durable when it is being tossed around in…lets say a backpack or pocket…as well as an accidental drop. I need to use something rubber or silicone or whatever works that is similar to products today that use these “bumper strips” to make the product durable. any suggestions?