PEX tubing has the ability to expand and return to its original shape. This makes PEX more freeze-resistant than traditional rigid pipe (copper, galvanized, etc.). Still, PEX is not freeze-proof. A PEX line can burst if fluid freezes in it. Freezing tends to be more of a concern in PEX plumbing installations, since no glycol antifreeze can be used for freeze/burst protection. PEX should be buried below the frost line in all direct burial applications. Insulation and pipe tracing cable can guard against freezing, as well.
All PEX tubing carries one of three grades: PEX-A, PEX-B, and PEX-C. PEX tubing is composed of cross-linked polyethylene. The grade assigned to each type of PEX reflects the method used to link its polyethylene molecules. PEX-A carries the highest grade. Cross-linking takes place while the polyethylene is melted, resulting in even cross-links throughout PEX-A tubing and producing an incredibly uniform material with no weak spots. This “Engel Method” makes PEX-A easier to work with and allows it to retain its shape. PEX-A naturally returns to its original shape after it expands or contracts.
Only PEX-A tubing works with expansion-style fittings and allows kinks to be repaired through heat application. PEX-A’s superior shape memory helps it resist freezing more effectively than the other grades of PEX. The bottom line: PEX tubing (especially PEX-A) is less likely to burst than rigid pipe if fluid freezes, but always take proper precautions to minimize the chances of freezing.