看了siceman版主的解释，我大体明白了，谢谢了。
佩服siceman版主的渊博知识，敬礼！
一下是转载siceman版主的帖子，再次感谢。

UPVC 全称聚氯乙烯，英文名为Unplasticized Polyvinal Chloride

PVC-U used to be called uPVC (for unplasticised PVC) but in 1990 the name was changed to conform to the international naming conventions for polymers. This was so that polymer databases would work correctly.

The standard international name of any plastic is now in two parts: the basic material name is given first and any special properties are given after a hyphen, ALL THE LETTERS ARE IN CAPITALS!

Low Density Polyethylene (old name - LDPE), Linear Low Density Polyethylene (old name - LLDPE) and High Density Polyethylene (old name - HDPE) are all types of polyethylene (PE) but would not appear to be such if indexed alphabetically in a database.

The new names have the polyethylene name first and the special properties second. The new abbreviations are Low Density Polyethylene (PE-LD), Linear Low Density Polyethylene (PE-LLD) and High Density Polyethylene (PE-HD). This means that families of polymers are kept together in a database.

The new correct name for uPVC is therefore PVC-U where PVC is the base polymer and the U refers to the unplasticised version of PVC. All the letters in the name are in upper case and PVC-u is incorrect!

If you see someone using PVC-u you now know that they are incorrect and dont know what they are talking about. Keep an eye out for it - even the most respectable people make the mistake