Tyvek is a strong & 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 Du Pont Tyvek which is virtually indestructible, incredibly waterproof, rip, tear & puncture resistant. For flat items choose a standard Tyvek envelope, see refs: PTY33C, PTY35C, PTY39C.