These 10 x 13 x 1 1/2 inch expandable Tyvek® envelopes are built from 18 lb spunbonded olefin — a material that outperforms standard paper envelopes in puncture resistance, tear strength, and moisture protection. The 1 1/2" side gusset lets the envelope expand to accommodate thicker contents without stressing the seams or compromising the seal.

The "First Class" designation reflects a clean, professional finish suited for client-facing shipments, sample distribution, internal document routing, and e-commerce fulfillment where appearance is as important as durability. Legal, medical, and publishing operations also rely on this format for multi-page documents and padded inserts that exceed standard flat-mailer capacity.

The self-seal peel-and-press strip secures contents without tape or additional equipment. Each case contains 100 envelopes, supporting consistent inventory for high-volume shipping departments. The parcel-friendly format ships without special handling requirements.