I have a question about how psychic crush work : rule wise there is nothing saying that armor does not apply, but how does armor can protect again an immaterial pressure (an un-warded armor of course) ? One of my player asked the question during a game, and I admit that I didn't have a good justification.

The psyker is squeezing the armour, not the person inside.

Except for a full energetic armor with helmet, no armor have rigid part everywhere, so it cannot protect against an immaterial pressure. Flexible par of the armor will be crushed with the person beneath...

Non-rigid armours generally provide a certain amount of cushioning. Otherwise, you might as well ask how flak armour protects against a mace. Hey, let's introduce even more damage types and assign armours different AP values depending on the type!

Er... thanks, I'll pass.