Quality Park Security Envelopes have a reflex blue pattern that protects sensitive client information because it obscures the details of the contents even when held up to light Single window envelopes display the recipient s address for simple bulk mailings These postage saver flat mailers are made from a more durable 28-lb paper than standard business envelopes so they will stand up to mailings Seam Type- Diagonal Flap Type- Commercial Trade Size- 6 5/8 Security Tinted- No