I am writing a Sci-Fi story that involves space ships shooting each other, as is the custom. I'm using a lot of handwavium, e.g. reactionless drives, FTL, gravity plating, etc., but I'd like the actual combat to be closer to reality. The ships mostly shoot each other with missiles from very long ranges, but occasionally get close enough to each other to shoot each other with projectile weapons strong enough to pierce each others armor.
I'm imagining a layered armor for the space ships that consists of multiple layers of plating and non-newtonian fluids. I also want to add a fluid/material as part of the armor layers that, much like a self-sealing bike tube, seals the armor against atmosphere loss if the damaged area is small enough, using pockets covering the inner layer of the hull to make sure larger damage, e.g. from a missile hit, doesn't drain the fluid from the whole hull trying to seal a ten meter hole.
Is there a fluid or other material that hardens to vacuum and might create a seal tight enough to withstand combat maneuvers or is one conceivable?