Your Woojer Vest Edge may get a bit warm during use (in a similar manner to mobile phones). Temperatures up to 110°F-115°F (43°C~46°C) are fine. However, it shouldn’t get too hot - to the point that it is uncomfortable to touch.
If you sense the temperature is getting unacceptable, lower the sensation level by a few steps. This will make the sensation more subtle, accurate, and pleasant for extended use.