Looks like the filters can be damaged by freezing.
You know, I'd read that more than a few places. Then the gf's miniworks msr filter fucked up and she went and scooped another one about a week before I was leaving on a sheep trip, and came back with the hyperfilter. Really not sure how a guy could fuck up and freeze one. Other than maybe if a guy was fucking around in some extreme cold and it froze as you were taking it out of the water and folded the filter or something maybe I guess, but if it's that cold, I'm heading home anyway.......