LUX 5 x 7 1/2 Open End Envelopes in 24lb. Bright White are perfect for invitations/greeting cards/thank you cards, sold as 500 per box..Comes in 24lb. Bright White.Dimensions: 5"L x 7.5"W.Sold as 500 per box.LUX 5 x 7 1/2 Open End Envelopes in 24lb. Bright White are perfect for invitations, greeting cards, thank you cards, and more!.Use this to send flat, bulky materials or multiple small items like coins, catalogs and jumbo cards. Flap is on the short side, helping to keep things from falling out after opening. Also called a “catalog” envelope, it actually comes in 39 sizes from tiny to huge, in white, traditional Kraft, and array of colors for special impact. Available with moistenable flap, some with self-stick Peel & Seal;. Also see our Open Side collection.