Is PEX freeze-break resistant?
PEX piping is freeze damage resistant and can expand and contract as water freezes and thaws within the tubing. No tubing material is freeze-break proof, however, and PEX should be installed using the same locally-prescribed insulation requirements to prevent freezing of any plumbing system.
Question and answer courtesy of Plastic Pipe and Fittings Association (PPFA). More information is available at: http://www.ppfahome.org/pex/faqpex.html