It's no secret that #10 security envelopes are the workhorse of business mailings, and Blue Summit Supplies standard #10 envelope with peel and seal flap keep documents safe and secure. Our most popular business envelope is made from durable 24lb white wove paper and comes equipped with a low-profile straight flap design, which makes it easy to fold and stuff up to 10 sheets of standard letter size paper with room for a #8 or #9 return envelope. Bulk carton package of 3000 envelopes offers great value to busy offices or large businesses.