A few years ago I was lucky to get my hands on some leftover tubing samples from work. I made myself a bulletproof flask. I’m sure this thing is tough enough to survive being run over by an eighteen wheeler.
The cap is made from a loose-bearing bottom bracket cup from a three-speed bicycle. The top is steel.
Titanium welds up very nicely under the right conditions. In many ways, it’s the material I’m most used to. It’s what I learned first.
This flask has a trick to it. The threads on the cap are left-handed. My theory is that if you have had enough, you’ll forget to unscrew in the opposite direction, and not be able to get in. In fact, I’ve inadvertently screwed the top down tight enough to need a large wrench to open it again.
This is a one-off item and is not available for purchase.