I see that Signature Plastics sells PBT caps for ALPS.
We use the same keycap vendor as Filco, so it should be easy enough to source caps, for anyone who wants them.
I'll look into PBT caps more, but from what I've read so far, there doesn't seem to be much difference. For what it's worth, this page claims that they're more prone to cracking and no less resistant than ABS to turning shiny...
PBT is harder (Higher youngs modulus, etc.) and as a result, more brittle. This is very frequently the case with materials. I believe that \KL (Keyboardlover) is incorrect when he says "There is a common misconception that PBT is less prone to becoming "shiny" over time than ABS, but this has been proven to be false." Who hav proved this? Where are their results. Another member did some testing, and while his test was less than 100% rigorously scientific, it does have merit. \KL is often at odds with that person, so he may have put it there. Another member, who reported putting 2,000,000,000+ keystrokes into akeyboard (and replacing the parts as they broke) said that he wore through his ABS doubleshot keycaps on his cherry keyboard much faster than the PBT on his IBM.
One good way to look at plastic wear is to examine spacebars. For example, the spacebar on my unicomp sees daily use, and it is nearly two years old, with no wear. I have some ABS spacebars that are showing some signs of wear after 6 months or so of use.
If you drop your keyboard, or hammer keycaps, you stand an easy chance of shattering the more brittle PBT, but this is because it is much harder, and therefore more wear resistant than ABS.
There are many legitimate reasons to have PBT, though I must say I prefer them for purely aesthetic ones as well.
