"The Sawyer Sqeeze is a legit Absolute One Micron filter. Even a single ice-crystal forming inside of it is going to be big enough to cause damage to pore size of the filter where the crystal formed - thereby turning it from an Absolute one micron filter into a Nominal one micron filter, or worse."
I can't disagree with you, especially because Sawyer says to discard if it freezes, but
When a water pipe freezes and breaks, there's a restriction like a valve. As the water freezes down the pipe, the water expands, there's no room to expand through the restriction so large force is applied to pipe and it breaks.
If an ice crystal forms in a pore, I don't think there would be huge force applied to the sides of the pore.
If the water in a tube froze, the tube would expand a little, but so what?
When you backflush the filter, the tube expands a little, include the size of the pore, which releases any particle entrapped. That's the same force as if it froze.
Sawyer's statement just says they don't know if freezing it would damage it, so just in case, throw it out if you think it might have frozen.
But, like you reported, it's common for backpackers to encounter freezing conditions.
If the filter is actually tolerant of freezing, it's too bad, because that's the one big problem with this filter.
But they just ignore it????
Sorry to rant - just a pet peeve of mine : )