Use the popular single window envelope for regular mailings The #10 remains the most popular size for correspondence and invoices. Create a custom window envelope to highlight your business when you order.

I recommend:  Order 500 to 100,000 of the #10 window envelope with bulk pricing at EnvelopeSuperstore.com. Get 24 lb. #10 with price breaks on 5 or more boxes of 500 at Uline. For a full line of single windows with your logo or return address, go to NEBS.

Use a double window envelope to show your return address Double windows give your bulk mailings the benefit of showing your address. Get lighter weight non-security envelopes for normal correspondence at lower prices.

I recommend:  For normal mailing needing a #10 in 24 lb. stock and price breaks on 5 or more boxes of 500, see Uline. Look at a full selection of size and window placement at NEBS. For orders up to 50,000 of 3 5/8 x 8 3/4 everyday envelopes see ActionEnvelope.

Get double window security envelopes for checks and invoices you issue Your Quicken, QuickBooks or other software used to print your invoices or checks typically needs a secure double window envelope that fits the template. Check your software specifications for the correct size.

I recommend:  See Check Crafters for either business size 8 3/4 x 3 3/4 inch or 6 1/4 x 3 5/8 inch for your laser printed checks; order 300 to 1800. Find security envelopes for checks with orders between 250 to 2500 at LaserPrinterChecks.com. Click “Double window Envelopes” to order 250 to 2500 regular or peel and seal check size at Compuchecks.com.

Find special size business window envelopes for larger mailings Select a 6 x 9 booklet or catalog 9 x 12 window envelope with regular or full face window to eliminate folding your documents.

I recommend:  Buy booklet window envelopes at 4envelopes.com. Find a large 9 x 12 window envelope with self-seal and security tint at 4envelopes.com; also full face window envelopes in various sizes at 4envelopes.com. See NEBS for booklet size with optional imprinting.