37.5® TECHNOLOGY works with your body to balance heat and moisture, creating a personally regulated microclimate of comfort. Hydrophilic active particles attract water molecules even at the vapour stage. They absorb the body’s IR energy giving water a reason to leave the particle. Active particles add an immense amount of surface area to the fabric and this allows fabric to evaporate more water exponentially faster. By actively responding to body temperature, these particles use energy from the body to accelerate drying rates – up to five times faster!