10 SELF-SEAL FLAT WHITE TYVEK® ENVELOPESDELUXE – 10 X 13 Resist tearing, puncturing and water damage with these self-seal mailers. Recommended for important documents and sensitive materials. Virtually indestructible – Tyvek® material is ten times stronger than paper. Save postage – Half the weight of paper. 14 lb. spunbound olefin.