Flying squirrels are not capable of powered flight like birds or bats, just like flying frogs and flying fish, they glide between trees. They are capable of obtaining lift within the course of their flights. Perhaps gliding squirrel is the most appropriate name for them.
Like most gliding mammals, it is active at night. Flying squirrels sleep during the day inside hollow trees, but also like attics and rafters of buildings.
The above clip from BBC demonstrates the Flying squirrels' amazing capability at moving through the woodland. Watch the stunning footage of these nocturnal creatures narrated by Sir David Attenborough.