Testing the Dynafit TLT6 vs TLT5 in extremely cold temperatures: -20F (-29C). The Dynafit TLT series of backcountry ski boots are ultralight, stiff in ski mode, and offer incredible range of motion in tour mode. They shave ounces with a lower total boot volume than typical touring boots. Some people are concerned that the lower boot volume will result in cold feet. We put those concerns to the test with a four hour at -20F in GTNP. Here’s what we found and a few tips for keeping fingers and toes cold when it’s ultracold out there.