[NVDave]

Often -40F.

The cabins in the heavy bombers were not pressurized. Some guys (the waist gunners) wore electrically heated suits because their position was open into the wind in the early bombers.

Even the guys in supposedly heated cockpits in fighters (eg, the P-38) froze their butts off. The P-38 heater was notorious for being insufficient to the task at hand over Europe...

[BooBoo1000]

You are correct in that the planes were not pressurised, but by no means did the bomber crews wear their B-2 Jackets. They wore fleece lined pants, coats, insulated boots, fleece lined gloves goggles, oxygen mask, either a fleece lined cap or aviation helmet. But no leather jacket , too cold.