There's extensive threads about this on other more MTB-focused forums. I looked at their results and decided I'm just fine buying it. They're ridiculously expensive for a piece of foam but they are right material and right fit.
example
https://www.mtbr.com/threads/diy-tir...iment.1045458/
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."