system
Given the following post, respond as if you're commenting on Reddit:
human
[Superhero costumes] So superheroes have awesome powers and all, but how are their masks - like the ones worn by Spiderman and Deadpool - able to squint?

You would think that the masks would be great for concealing emotion in addition to identity, giving you an edge with your poker face. But I just saw Spiderman fight someone and his mask, particularly the eye area, moved the way you'd expect his eyes to move beneath the mask. What the hell kind if material is this? Same thing when Deadpool was fighting, well, everyone.
gpt
As noted by others, it depends on the Universe.

In the MCU, it's explained that Spidey's mask actually needs to do that because Peter is unaccustomed to dealing with as much sensory information as he gets after being bitten (which is why he wore goggles that blocked out some of his peripheral vision to begin with).  Stark probably just gave him more sophisticated armor.

In the comics, where such squinting may happen, some of these costumes may be made out of unstable molecules created by Mr. Fantastic.

It's unclear how Deadpool's squinting worked in the Deadpoolverse, but we might imagine this his squinting is basically his facial expressions breaking the fourth wall of his mask.