Thank you for your reply.
The membrane will be penetrated by array of little metal pins acting as a punch (each pin of diameter approx. 1mm and pins in array 3x3, pins very close to each other). Pins will be pushing the membrane into corresponding holes in a plate/matrix. Obviously proper tolerances maintained will prevent the membrane being squeezed by pins against side walls of holes in matrix.
The membrane will not be in contact with water.
I need to be able to make the membrane myself (by casting it properly) despite that some sheet silicone/rubber materials are available on the market.
Thanks.
you also forgot to mention what the membranes intended use is, most silicones are not recommended for continuous water submersion
if your building a shower pan there are waterproof membranes available
