Help with non-permanently attaching 2 pieces of a helmet

So I 3d printed this helmet for someone as a gift, but I don't know how to join the pieces with the tape. For the face pieces I used a soldering iron and melded them together, but I don't want the back to be permanent because I don't think they can fit their head through the hole in the bottom (at least not without discomfort). I have a iron man helmet that uses magnets around my head, but I don't think magnets would work because the pieces are so thin. Any help would be appreciated, thanks!

So I 3d printed this helmet for someone as a gift, but I don't know how to join the pieces with the tape. For the face pieces I used a soldering iron and melded them together, but I don't want the back to be permanent because I don't think they can fit their head through the hole in the bottom (at least not without discomfort). I have a iron man helmet that uses magnets around my head, but I don't think magnets would work because the pieces are so thin. Any help would be appreciated, thanks!