The most important difference between PolyVinyl Chloride U and C piping systems is temperature resistance. PVC-U can be used up to +60 °C if creep and relaxation are taken into account. The permissible load is, in that case, limited.
PVC-C has been chlorinated and therefore the material can resist a higher temperature, namely, +80 °C. This is why PVC-C is sometimes referred to in the jargon as "High Temp PVC". As well as being wire welded, PVC-C can also be perfectly bonded with special PVC-C adhesive.