Comment Comment by dgacmu They're all design 1. Here's a manufacturer link with an air flow diagram for one of the recommended ones: https://www.ergodyne.com/nferno-6970-extreme-balaclava-hot-r...That said, the volume of air that could be retained in the foam heat exchange insert is quite small (eyeballing it, maybe 50-100ml?) compared to normal human inhalation volume, about 3-4L per breath during moderate exercise. parent dgacmu 2 years ago
That said, the volume of air that could be retained in the foam heat exchange insert is quite small (eyeballing it, maybe 50-100ml?) compared to normal human inhalation volume, about 3-4L per breath during moderate exercise.