I have a 1L platypus (platy bottle) but I've never used it in cold weather, will the plastic crack if it gets cold??
No..
if not, am I able to keep water in it and let it freeze??
Yes, but realisticly, if you actually do let it freeze, it's kind of defeating the purpose - a big hunk of ice in a platy doesn't lend itself to drinking.
it seems pretty tough like it could handle being half full and frozen. Does anyone have exp. with this??
I use my platy's in subzero all the time. if I keep them insulated and keep the mouth from freezing up they are ok.
In seriously cold conditions I switch to nalgenes because I can put *HOT* water into it without hurting it. I don't put hot water (From melting snow) into a platy..