Manufacturer Part Number R1580. Lightweight 14 lb Tyvek. Seam Type: Center; Flap Type: Square; Trade Size: 13 1/2; Security Tinted: No. Exterior Material(s):DuPont Tyvek Basis Weight:14 lb Tyvek. Quality Park Open-end Envelope – Catalog – #13 1/2 [10″ X 13″] – 14 Lb – Peel & Seal – Tyvek – 100/box – White (R1580_40).