Save the time and effort to write or print addresses on the envelopes by getting window envelopes. The 6 3/4 white window envelopes are great for mailing invoices, letters, and other official documents. These envelopes are made from 100% acid-free 24 lbs stock paper. This is the standard paper quality used to make most office envelopes as it’s both durable and cost effective. When ordering, businesses can upload their black and white company logos and get them printed for free. The flaps of these envelopes are lined with moisture-activated gum for fast sealing. These envelopes can be printed upon using inkjet and laser printers. These are also typically used as return envelopes.