You have to tape them to seal completely. when you peel the strip to seal it the gum doesn't come to edge leaving to much room for it to be opened by anyone or even the postal machine that the mail goes through.
Staples 10" x 13" White Wove QuickStrip™ Catalog Envelopes 100/Box Staples 10 x 13 White Wove quickstrip catalog envelopes worked very well in mailing polo shirts to my clients without a lot of weight therefore allowing me to save in postage. Big enough for one polo shirt yet cost effective all around. They are also strong enough to hold one shirt to be mailed effectively. Would recommend these envelopes. They are cost effective and good quality. Staples has a good product and easy to use!
Paid extra to get the envelopes that don't need to be moistened. They were supposed to be sticky - you peel off the tape and press to seal - but the glue was not sticky. I had to tape them shut. I also thought it was strange that the box was not sealed in any way. Someone could have taken some of the envelopes out and stolen them. I opened the box before buying and it looked full. Other than those two problems the envelopes were fine.