I have a sample coming from a company that “talcs” their silicone rubber sheets. Its standard practice apparently and a sheet 1mx0.7m should cost no more than £20.
They add talcum to the silicone as its cured/heated/rolled (cant remember) which creates a kind of tracing paper look but it has the properies of rubber.sounds like a winner to me.
Will let you know how goes when arrives.
if on top of that i could find an acetate type material which blocks ambient ir we could be cooking.
O