Envelope is made with a material that inhibits the growth of the product 9 x 12 envelopes are perfect for storing and mailing full size 8-1/2 x 11 sheets of paper, letters, documents, catalogs, photo's and other home and business mailings Quality Park's 28 lb. white wove stock creates a professional touch to your personal and business mailing Redi-Strip closure provide a seal to keep contents contained - simply peel off strip and press So many uses means supply is depleted quickly - conveniently packed in 100 count to reduce frequency of purchasing