10 x 13 Booklet Envelopes Open Side Envelopes - Bright White 28Lb - 50 per Pack Business Envelopes (10x13) 10x13 Booklet white Multi-purpose envelopes. These Booklet envelopes standard 28 lb white stock Has Moisture activated gummed seal. Great for mailing out sales brochures, annual reports, and product literature 50 Envelopes per pack