We discussed this among ourselves when in kindergarthen and school while doing the mandatory skiing classes. The most sensitive part is the nose so you breath out there to warm it up. Less dripping nose as long as you can keep it up. If you forget, the nose directly freezes up and your nose will be dripping the rest of the trip :-)

I was so baffled that the heat exchangers were so cheap, I had always imagined them to cost a fortune so I didn't even think of getting one until a few years ago. But I guess they did cost a lot more 20 years ago...