Quality Park #10 security envelopes (4-1/8 in x 9-1/2 in) are a staple for your private business mail; our secure, self sealing envelopes have Redi-Strip press-to-seal closures for maximum convenience Security envelopes shield identification numbers and private data with a special security pattern to scramble the appearance of text; keeps envelope contents safe from prying eyes, even if held to light Redi-Strip self sealing envelopes let you fly through mailings in record time; just peel the strip and press for a strong, durable seal Each letter sized envelope is made of 24 lb white wove paper with #10 envelope dimensions (4 1/8" x 9 1/2"); side seam construction gives you a large area for labeling, printing or hand addressing #10 envelopes are a never-out office classic for a reason: these workhorse envelopes are economical, versatile and convenient for offices, businesses and schools