Tyvek Pocket Gusset Envelope C4 Peel and Seal Plain 38mm Gusset 55gsm White (Pack 100) Extra capacity, ideal for mailing really bulky and awkward shaped mail. Amazingly light, water resistant, tear resistant and burst resistant envelopes that stand up to the sort of rough handling expected during mailing, shipping and delivery. Size C4 (324x229mm). Gusset size 38mm. Packed 100.