My fiance and I are getting married and needed to send out the invitations. The outer invitation sleeve had swarovski crystals that were causing tears in the envelopes during shipping (we mailed one experimental one to a family member that arrived with holes). I racked my brain trying to figure out how to keep it all intact. I came across this on Amazon and thought I’d give it a try. It’s very light but provides some cushion within the envelope. With the help of this stuff, our invites arrived with minimal damage. I don’t know what purpose this stuff has, but it worked and was a Godsend.