I mean the Adafruit pixels. There are hollow pixels - IP 65 and filled pixels - IP 68. I understand that strips only bend up and down. The pixels have wires that allow much greater flexibility.
You’re totally right. I was assuming the Adafruit ones were IP68 rated because they LOOK so freakin’ waterproof. THANK YOU for that, you just turned a whole mess of long-term frustration into a little bitty pile of short-term frustration. 
If these types of pixels work for you, consider asking Ray WU (http://www.aliexpress.com/store/701799) if he can make a custom set for you. I would ask him to use silicone rubber insulated fine strand wire (the type used for remote control hobbies). The silicone insulation and fine strand cables are much more flexible and are meant to bend (Remote Control vehicles put lots of stress on the wires) when compared with standard PVC or other plastic insulated wires.