Security business envelopes feature a blue inside tint to protect your privacy. Redi-Strip on the flap provides a clean, quick seal immediately upon contact. Simply peel off the adhesive strip and press to seal. The peel-off strip protects the adhesive from dust for a longer shelf life. No. 10 envelopes include a high-quality poly window for your mailing address, white wove 24 lb. stock and a contemporary seam.