S = 20-piece pack, M = 100-piece pack.Safe Storage: All 6 x 9 mailing envelopes are packaged in a firm box and are easy to store. Manilla envelopes 6 x 9 with clasp are made paper, and for mailing small size paper documents, manuscripts, announcement files, crafts, photographs, books, invitations, magazines and so on. envelopes protect the of your contents double metal clasps and moisture-activated adhesive seals keep scripts, photos, or other items secure whether they are shipped in bulk or stored ideal for work or personal use. Weight: 0.4 pounds.