A vacuum pump that traps particles on its cryogenic surface to achieve high vacuum up to ultra-high vacuum. It works very fast and can adsorb almost all kinds of molecules, creating a very clean vacuum. Its cooling head is often coated with a highly adsorbent material such as zeolite or activated charcoal to increase its capacity. Liquid helium is typically used for cooling, but liquid nitrogen or other refrigerants may also be used. The adsorption material of the cooling head becomes saturated over time (too thick a layer of adsorbed material poorly dissipates heat) and must be regenerated. The pump is disconnected from the space it has evacuated and heated up so that the adsorbed gases can be released and sucked away. After cooling, the cryopump is ready for operation again.