The 'PVC' part of PVC-U stands for Polyvinyl Chloride. The 'U' stands for Un-plasticised.
Find some quality info on this subject with some technical background at
http://www.thewindowman.co.uk/pvcu.html
Companies are always saying their pvc is best - but in my opinion most pvc-u window systems use pvc-u of very similar quality overall - the differences come down to the thickness of walling in pvc-u extrusion ( typically 3 - 3.5 mm) and the depth of frame (60mm, 65mm, 68mm, 70mm) not the QUALITY of pvc-u. IMHO!
PVC-U can be recycled -
http://www.thewindowman.co.uk/recycling.htm
Some is also regrined for use in pvc-u windows again
http://www.thewindowman.co.uk/regrind.htm
From the last link you may like to inparticular note:
In some parts of Europe, notably Germany in particular, it is already a Government policy to insist on the use of recycled PVC in window profiles, and many extruders in the U.K. are also keen to commit themselves to the principles of ISO4000 which covers environmental issues. With 'green' concerns in mind nobody should have any real objection to their being a content of up to 10% regrind in their new window and door frames. Indeed in the not too distant future, with facts understood, and with the expansion of the environmental conscience, I can almost hear my customers saying to me: "can you reassure me that your windows contain at least a small percentage of 'regrind' - because I care about our planet, you know, and I understand the windows will be just as good".
