>I suspect in normal use the ball would bounce off the page, avoiding smears.

>Plastic is pretty soft and gummy when you get down to it.

I don't think most people could break the typewriter ball with their bare hands, either by pulling or compressing ("squishing"). Just tried this with my least-favorite font — 275lb blue-collar electrician can't break it (barely any deflection).

Not sure what the plastic's composition is, but it is absolutely RIGID (as it must be). The thing can fly letters onto the page (I can do sustained 80wpm, with bursts into 100+ — thing could go twice my output rate on a clear-headed day, mechanically).

Selectrics are just absolutely modern marvels (still)!

>engineering resin

The ball's plastic is harder than cured JB-Weld™ (standard 2-part mixture).

Oh yeah on a human scale there's plenty of VERY hard plastics.

It's still pretty soft and gummy when compared to a LOT of materials. It's all relative and whatnot. You'll often find machinists using descriptors like "chewing gum consistency" for stuff like copper. On that scale plastic is pretty soft and squishy.