3-Up 1099 Envelopes fit the three per page 1099-NEC forms for easy mailing of tax documents. They are made with 24 lb. white wove paper with enhanced security features. Envelopes have a security tint and pattern to protect private information from view. Double windows fit NEC forms precisely so private information remains concealed while displaying addresses. Self-seal envelopes have a peel-and-seal strip for no-fuss mail prep. Go from desk to mail bin in minutes. Envelopes read "IMPORTANT TAX RETURN DOCUMENT ENCLOSED" on front to alert recipients.