Poly envelopes offer a lightweight yet durable construction that resists moisture to protect your valuables from the elements. Heat-welded seams make envelopes more durable and long-lasting than traditional paper envelopes. See-through design allowseasy identification of the contents. Top flap seals securely with a hook-and-loop closure that allows quick fastening and releasing of the envelope flap. Reusable envelopes are made of durable polypropylene and are stain-resistant and tear-resistant. Poly material is acid-free, PVC-free, lignin-free and archival-safe.