While this method is commonly used in simple cryogenic systems to cool objects down to 1 K, it is also fairly popular in more complicated cryogenic systems to bootstrap to lower temperatures. For example, in a He refrigerator, condensed He (a rare isotope of helium) is evaporatively cooled and can attain temperatures as low as 200 mK. But the He must be condensed to a liquid first, and a 1-K pot is typically used for this purpose.