Tyvek is a strong and durable material that will withstand the most gruelling conditions so is suitable for all your important postings. It is a lightweight but heavy duty envelope that is puncture resistant. Available in a range of standard sizes so you can find an envelope to fit your needs. Manufactured from 55 gsm DuPont Tyvek which is virtually indestructible, incredibly waterproof, rip, tear and puncture resistant.