Pym Particles (also known as Cross Particles) are subatomic particles of an extra dimensional nature that are capable of shunting or adding mass and reducing or increasing scale of any form of matter, compressing physical forces around such objects or organisms that they are applied to, as well as increasing density and strength of the subject.

The particles were initially created in the 1960s by scientist Hank Pym, who aided the intelligence organisation S.H.I.E.L.D. by harnessing the Pym Particles using a custom suit to become a field agent known as Ant-Man. His wife Janet van Dyne also aided him under the moniker of Wasp.

Despite Pym wanting to keep the Pym Particles a secret, Pym's former protégé Darren Cross managed to successfully recreate the Pym Particles in 2015, using it to create the Yellowjacket Suit, which he planned to sell to terrorist groups such as HYDRA and the Ten Rings.

Human users of technologies that harness the particles are able to shrink themselves to the size of an insect, while still possessing the physical resilience, as well as effort and force exertion capabilities of an average-sized human, which can be amplified in their reduced scale.

The process of altering size compresses force and energy, manifesting as brief shockwaves of vibration around the target, which enhances the amount of force the target can generate. It also enhances the density and resilience of a target, making them stronger and harder than normal. Living subjects of this develop inhuman effort and exertion capabilities, notably giving them the force of a bullet while shrunk.