It's even too cold for Chicago's resident polar bear.
The city's Lincoln Park Zoo says its polar bear, Anana, was kept inside Monday because of the record-low temperatures.
Zoo spokeswoman Sharon Dewar says that while the below-zero weather might be comparable to what polar bears experience in the wild, Anana doesn't have a thick layer of fat that bears typically get from eating things such as seals and whale carcasses.
That extra insulation would make it uncomfortable to live in Chicago during the rest of the year, so Anana gets a different diet.
While she stayed inside, Anana lounged in her comparatively balmy indoor climate that's kept at 4 to 10 C.
Anana usually has access to both an indoor and outdoor area. She'll be allowed to venture outside Tuesday.