Founded in 1939, Seaboard Envelope Co. Inc. is one of the leading manufacturers of envelopes in the United States. Based in Irwindale, Calif., the company prints a variety of envelopes, including square flap, side seam, regular/business, pointed flap, poly window, catalog and open-side, booklet envelopes. It specializes in inline/offline custom printing as well as flexo and jet printing. Seaboard Envelope Co. Inc. specializes in custom adhesives like peel-to-seal and latex. The company converts customer supplied preprinted and unprinted sheet stocks.