Good question. I only have experience with one pouch, which was John Bull Royal English. I read beforehand on TR.com about how moist it is out of the pouch, and God only knows how long it was aging for (got it from someone else). I just kept it by itself in a ball jar until I was ready to dig into it, and when I did, it was still very moist. From this limited experience, I assume those seals are pretty good. I'm going to defer to the more experienced guys on here. Interested to hear their opinions on this.