Wirsbo does not warrantee tubing against freeze damage. Freezing can damage the tubing and cause early failure due to stress. The fittings can be damaged by freezing. Pex does reform from ‘memory’ at 270F or so, but it will not be reformed otherwise and repeated freezing will make it burst. If it is insulated to prevent freezing the use is excellent, but so is copper. Pex offers freedom from galvanic corrosion, acid resistance, and flexibility, but it can be damaged by hydrocarbons in asphalt, soil, paints,etc.