Penetration is the stat that represents a weapon's projectile's ability to penetrate walls of various sizes. Projectile power and class are the determining factors for a weapon's penetration power, with higher projectile power allowing for more penetration. Only bullet-class weapons have the ability to penetrate walls, as plasma, rail, and explosive projectiles have no penetration. The maximum penetration a weapon can possess is four blocks. The Ray Gun C-01y, Pistol C-01p, Alien Rifle, and Sniper Rifle CS-YippeeKiYay all have four-block penetration.
The standard penetration of bullet weapons is three blocks. Penetration can also depend on upgrade level. The amount of blocks a weapon can penetrate is also not uniform, weapons with the same number of block penetration capabilities with different projectile powers will have different performances at different angles. For example, both the Shotgun CS-DAZ and the Shotgun C-01s have a penetration power of three blocks. However, the C-01s possess a higher projectile power of 1.1, compared to the CS-DAZ's 0.9, meaning the C-01s has the ability to penetrate three block walls with a greater variety of angles.
Exceptions to the bullet class only rule include the Grenade Launcher CS-SpamThemBaby and the Drone Gun CS-Virus. These weapons lack penetration qualities, but can still glitch through thin walls. This is accomplished by running against the wall and firing them, allowing the projectiles to then glitch and appear on the other side of wall.