The answer to this question depends on what you mean by “freeze resistant.” PEX (cross-linked polyethylene) is unique in its ability to expand when water freezes inside it and resilient to shrink back to its original size after the water thaws, avoiding fractures and leakage. It is not totally immune to rupturing from the expansion of water freezing inside it, but very resistant, as proved by testing over multiple freeze/thaw cycles.
Water inside uninsulated PEX pipe, however, freezes when the temperature dips below 20º F for a few hours, just like any other pipe material. The difference is that you can’t electrically thaw it like copper pipe. Also, thawing with any kind of high-heat blower is risky. So while PEX pipe will most likely not be damaged by a hard freeze, you may have to wait for it to thaw out on its own or gently warm it slowly before you can get water flowing again. For this reason, manufacturers recommend that PEX be insulated in any unconditioned spaces of freeze-prone parts of the country, the same as other pipe materials.
While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
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