The bottle appears to be of a sturdy polycarbonate construction that is molded into the shape of a 'TIKI' charm. The bottle has an attached cap so it can't be lost and can be clipped in. The bottle comes in several colors (red, blue, purple, orange).
After purchasing the bottle, I started my standard test which involved filling the bottle 3/4 full of water and placing in the freezer.
I never used the bottle on any hikes, I did take the bottle and place it inside my ice chest for base-camp cooling/water storage on several occasions.
Regrettably, after about ten freezing/thaw cycles, the bottom of the bottle budged out and cracked across the entire bottom. I first knew there was a problem when I took the bottle out of the freezer and it would not stand-up due to the deformation of the bottle from the ice expansion. The bottle had never been dropped, however I did notice a slight defect in the bottom of the bottle, it was a rough spot where I believe the polycarbonate was injected into the mold. I'm not sure if this is the reason the bottle failed, but I have my suspicion.
I have sent email to the vendor and I'm awaiting a reply to see if this is a long standing issue with the bottles. Until I get feedback, I can't recommend this bottle for any activity (winter usage) where the bottle might freeze solid.
* * * * * * * * * * * * * * * * * * * * FOLLOW-UP INFORMATION as of 8/19/04: After contacting the vendor (Bisonbelts.com) I was told that *some* of the first run of bottles may not have been made out of Lexan. I believe that when I examined the bottom of the bottle that failed, the recycle triangle was stamped with a "PC" indicating the bottle was indeed made of polycarbonate.. However, I received conflicting information about the bottle specifications from REI staff members. One representative I talked to at the Northridge CA store said that the “Stone Master” bottle was a “novelty” and was not made to be frozen. I told her that I disagreed because the REI web site indicated the bottles were made of Lexan. Another REI representative I contacted via email stated that the bottles were made of Lexan and could be frozen, and that I may have received a defective bottle. The jury is still out on this product, and I guess I will never know the truth, as I have asked Bison Designs to send me a replacement bottle that has a more conventional shape (round). I will report later if I have any trouble with the new bottle.