Jon Lung rigged up some small fans inside his homemade face shield to defog the mask while riding in winter. On Instructables he writes:
Looking for a way to protect my face from harsh winter conditions, without enduring damp scarves pressed against my mouth or the excessive, mummy like, wrapping of my head, I created headgear with a magnetic visor that is defogged by tiny 5 volt fans.
This instructable will guide you through the process of making a Mk. 1 Winter Face Shield. As a fair warning, it is an involved project that involves programming, sewing, and some various fabrication and building. This process is much easier if you have access to a shop space with tools like table saws and belt sanders. If all you have are some hand tools and a back porch to work in, various details can be scaled to fit your capabilities. We can still do this.
Every Wednesday is Wearable Wednesday here at Adafruit! We’re bringing you the blinkiest, most fashionable, innovative, and useful wearables from around the web and in our own original projects featuring our wearable Arduino-compatible platform, FLORA. Be sure to post up your wearables projects in the forums or send us a link and you might be featured here on Wearable Wednesday!