Breath ability is very important to clothing comfort but are the best fabrics breathable enough? According to the eVent web site we can produce 0.25 to 0.5 liters of sweat per hour just walking and as much as 1.5 liters per hour if working hard. Other sites indicate that much higher sweat rates can occur with the highest ever recorded being 3.7 liters per hour by Alberto Salazar in the 1984 Olympic Marathon! According to these independent lab results eVent breathes at about 5 liters per meter squared per 24 hours. If we generously assume that 4 meters of fabric are used and that the sweat is evenly distributed across that area (not true), then in ideal lab conditions eVent can cope with about 0.83 liters of sweat per hour, which may not be enough. This study shows that the back can generate approximately twice the sweat of the arms, overloading some areas of the fabric well before the previous figure indicates.
How much we sweat is a function of our core temperature and not just activity level. When we dress for cold conditions and then work even moderately hard our core temperature can shoot up dramatically. This is why adjustment of insulation is so important. Vents allow cool air into your clothing system without needing to take garments off, reducing the amount you sweat (as well as increasing breathability). FurTech garments use vents that allow air past the integral insulation directly to your base layer.