Or, you could take keys, ABS and PBT that have been cast in the same mould, and weigh them on a sensitive digital scale ... I think that this would be very unusual, but I have just that:
Key 1: Black 6-unit space bar from a set of double-shot Cherry keys from a Cherry G80-11900 keyboard. Curiously enough.. it has the markings ">PBT<" and "2" in it. I have done the acetone test on it, showing that despite its markings, it is not PBT and probably ABS.
Key 2: Light grey 5-unit space bar from a winkeyfull Cherry G80-1800. It also has the markings ">PBT<" and "2" in it. Acetone test was made, showing that it is PBT.
Except for the colour, both keys look exactly the same, but when I measure them I see that the ABS space bar is 1.1 mm longer than the PBT space bar. I tried it on the G80-1800, and it does not fit.
The weights:
ABS key: 5.62 g
PBT key: 6.65 g
6.65 / 5.62 = 1.18327...
Conclusion: PBT is 18 percent heavier than ABS.
However, it should be said that ABS is a blend of three plastics and that the composition varies a lot between blends. All keys will also contain pigment and a difference in pigments could also affect the weight.
This comparison I made is also a bit inaccurate in that because PBT keys are probably cast in bigger moulds to account for PBT shrinking more after demoulding, making these even heavier.
I did also look at other PBT keys from Cherry, but I could not find any larger keys that were exactly like my double-shot Cherry keys. When I weighed those that were sort-of alike, PBT keys were around 16 percent heavier.
