I sealed three crisply folded copy paper pages into the first envelope and left it on my office desk for mailing later. Within a short time I noticed the flap was releasing so I pressed it down again but the problem repeated and I had to add scotch tape. I'd like to believe that this was just one bad envelope and not have to repeat this step for the next 99 mailings but why take the chance? Next time I'll pay a little extra for the name brand alternative.