Engineering360: "Smart Balaclava Heats Air"

When I would run in bitter cold weather I would wrap a heavy knit scarf around my face. It would act as a heat exchanger by collecting the heat when I exhaled and warming the air when I inhaled. When it got moist from my breath it would work even better.

Sounds like a good solution in extremely low temperatures, but for more moderate temperatures wouldn't a much less expensive, and self powering solution be to incorporate phase change material into hollow fibers, so that heat from exhaling would pre-heat inhaled air?