The lighting Gels are a (paper) thin sheet of polycarbonate/polyester and can be placed in front of lights to give a nice colour effect. Filter Gels are made so that they can withstand high temperatures.
Colour Transparent Acetate Heat Resistant Lighting Filter Gel Sheet Crafts Film
JEJE Heat Resistant Transparent Acetate Sheets
Heat-resistant silicone rubber HB for tin casting, heat-resistant up to 450¯C
Prym Heat-Resistant Silicone Ironing Mat, Pink, Craft Supplies