The standard adiabatic laps rate for moist air is 3°F per 1000 ft of altitude. So if Berlin was 50°F, at 28,000 it would be about about -34°F. Even if it was 70°F in Berlin, it still would be 10 below zero (-ish) at mission altitude.
And if you’re old enough to remember the era before when things like battery-powered socks became reliable, you’re probably amazed everybody in the crew didn’t freeze to death on every mission.
Air crewmen must’ve thought Christmas had come early when the B-29 arrived because from that point on all bombers were pressurized. Just like the modern airliner, the crew rode inside a sealed and climate-controlled “pressure vessel,” and maintaining the integrity of the pressure vessel meant that all the defensive guns had to be controlled remotely, not by an airman in a heated suit and standing in an open window.
But the article also states,
(Above: As the first US bomber to have a pressurized cabin (and it wasn’t sealed well, frankly,) was the B-29, crews risked all sorts of oxygen depredation issues: hypoxia, altitude and decompression sickness, and barotrauma and that risk was high and dangerous, and all the bomber crews got was an oxygen mask…that often didn't work, or froze up. See those flak vests developed in ‘43? 32 easy pounds.