It is strongly advised against letting your filters freeze. Similarly, it is strictly discouraged to store the elements (even unused ones) in very cold climates. Residual water inside the element will expand and consequently enlarge the pore size, eventually destroying the element. Whether your filters are unused or already used and completely dried, a small amount of moisture could still remain inside, especially in predominantly humid climates. This moisture could expand inside the filter and render it unusable. Please note that this recommendation applies to ALL Berkey elements, including the Sport Berkey bottle. Freezing your element and making it unusable will also void your warranty coverage.