The "seal" on these envelopes is a joke. Without adding a strip of tape to the flap there is no way to be certain that the contents of the envelope would arrive intact. Usually I've had luck opting for the Staples brand products but this is certainly one to avoid.
About half of the envelopes had a very weak seal... I had to use packing tape on all of them to insure the contents wouldn't be lost in the mail... wasn't happy... Bought the same envelopes two years ago and didn't have this issue...
I would not order these envelopes again. I purchased them for the easy close feature and they did not stay closed at all. I had a mailing for 250 pieces and had to go back and tape every envelope. I was very disappointed.