The typing experience is made of the switch type, the caps material and their weight, the case material and its weight and if the assembly has a plate or not, and even the material and thickness of it. The experience includes the feeling and the sound perceived.
In general, the heavier caps, plate and case will reduce high frequencies, while the lighter assembly will increase them.
Density or specific gravity accounts for the overall weight of the caps depending on their volume:
ABS ranges from 1.04 to 1.12 g/cm^3, depending if it is blended with other materials. There are for example ABS, ABS-PA, ABS-PC, ABS-TPU. I do not know if caps manufacturers use blended materials. Acetal, also known as Delrin or POM, is 1.42 g/cm^3. PBT ranges from 1.31-1.72 g/cm^3. Therefore PBT and POM, depending on the specific plastic blend used, are the materials with higher specific gravity.