Asphalt

What you want is "minicell" foam. It can be bought in sheets and it can be had in virtually any thickness you want. You can also get it with peel and stick adhesive backing. It's what is used to make seat pads for road racing motorcycles, kayaks, etc. I would recommend you go with the non-adhesive version for your race seats. You can cut it and shape it (shape with a Roloc disc or a sheet of sandpaper for more precision) and then install with spray adhesive, or adhesive Velcro. The Velcro allows you can remove it if you like or swap thickness to adjust for different drivers. In the size/quantity needed for seat projects it's best to get it from a direct supplier and skip Ebay/amazon. I am not sure the rules on linking suppliers/vendors on this forum, but if you PM me I can offer you a link.

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