All About Invoices offers professional compatible envelopes to work with the invoice you've chosen. You'll have the opportunity to select a matching #10 single or double window envelope as well as the ever-popular standard #10. All are constructed of dependable 24lb. white wove stock and gummed flaps. In addition, Business Reply Envelopes in two sizes, #9 and #6-3/4, are available to speed payments.