there are non-silicone flexible foam products commonly and cheaply available; these are used as weatherstripping for door and window frames in houses (sold in hardware stores) and for sealing gaps between the sides of a pickup truck bed and a camper shell (sold in auto supply stores). of the foam sealing materials available, the highest quality ones are used to fabricate replacement door gaskets for cars, but these require application of an adhesive to stick them together since they do not have stickytape on one side. Both home and auto products are usually sold in narrow rolls and have stickytape on one side. They come in different roll widths and foam thicknesses. Please note however that because they are foam, they consist mostly of air and hence are not very thermally conductive. all of them are good electrical insulators. Another possibility is foam-core doublesticky mounting tape from 3M. This is thinner than the gasketing material described above and the adhesive used is extremely strong, and on both sides of the tape, but the product is a lot more expensive than door gasket. It is available in roll form at industrial supply houses or as precut squares (as for sticking things like towel racks to walls) in hardware stores.