Pop-out pads underneath the sole extend to give you extra traction and cushioning, then retract when you don't want traction and cushioning. The pads are moved by way of a set of micro-compressors, which pressurize a set of interconnected cavities to about 2.5 bar (36 psi) to pop them out, then release the pressure to let them back in.

[Source: New Atlas. 5 January 2020. Loz Blain]