DSF

If you look at the bill/peak of the cap you will see some text. ( Roughing it Smoothly) . This is made from a rubber like material about 1mm thick. It could be made with a mould or it could be cut using a thick vinyl and a Tangental cutter.
However its made , its very effective.
Anyone any idea how its done?

It looks like a vinyl type material that expands once heated. Just press it normally and watch it 'rise'.

the first time i saw this i thought it was some type of extruded plastic, but now is suspect it is an expanding thermal vinyl