... humidity, ROSH Fr-4 Epoxy Glass Cloth Laminated Sheet (FR4 sheet,FR4 insualtion parts)is made of electrical non-alkali and non-wax ... cloth impregnated with epoxy resin by procesing under ... is applied to electricmotors,mechanical lines,electron lines and electrical appliancelines,PCB test,transformers,ect.Fr4 is flame retardant.