Tyvek * envelopes are very tough, durable and lightweight. Ideal for sending important documents or heavy or awkward shaped items. Also available in gusset sizes. Use For, Postage of bulky, heavy or confidential items requiring strength and security. Where water or grease resistance is important. Techniques, Ball point/pencil writable. Also receptive to adhesive/gummed address label. Some grades printable by flexo/offset litho overprint. Pre-test required.