At this point we haven't done any testing in extreme cold to say whether the can will freeze or not. The lines in our catch can kit are closely modeled after the stock PCV line, so if the stock lines don't freeze it is highly unlikely that our hoses will freeze. Also, while there may be small amounts of water vapor on the inside of the hoses that could potentially freeze into a layer of frost, it would hardly be enough to completely block the off line. Blow-by contains enough oil and fuel that it is doubtful that the contents of the can will freeze. Still it is recommended that you check the can more often as it is common that catch cans collect more contents in winter temperatures.
Let me know if you have any other questions!
-Sara