You are looking for a product called "reticulated foam". That is foam with all the cells "popped" (no bubbles) so water and sound would just run through it. Wilson and many other manufacturers use it for speaker grills. It will stick quite nicely to Velcro.
You can buy it in various densities and sheet thicknesses at most foam suppliers. Generally, the foam color indicates its density, so you don't have much choice there.
I'm not sure if it can be sewen (to make a sock) but there are special adhesives that you could use to join it at the seams.
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You can buy it in various densities and sheet thicknesses at most foam suppliers. Generally, the foam color indicates its density, so you don't have much choice there.
I'm not sure if it can be sewen (to make a sock) but there are special adhesives that you could use to join it at the seams.
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