No. 10 invoice envelopes offer a self-sealing design that makes envelopes quick and easy to close. 24 lb. envelopes require no moisture to seal. Unique double-flap design keeps the gum from sticking before use. Simply raise the lower flap and press. • Self-sealing design allows quick simple closure. • Double-flap construction prevents gum from sticking before use. • Sturdy 24 lb. stock withstands abuse during transit. • Perfect for businesses schools personal use and more. • Sold as 500/Box.