Clear 6mm UV Stable Twin-wall ?Premium Grade Polycarbonate. Tough and durable enough to withstand the knocks & has superior thermal efficiency over glass. Covered by 15 year warranty against breakage and discolouration. Insulating double layered, thermally efficient, keeps the warmth in and the frosts out. Safe, secure and virtually unbreakable and is significantly safer around children and pets. Diffused light won't burn plants and great for seedlings.