DownpourHydrophilic membranes control the micro-climate inside the garment by absorbing and dissipating sweat through the diffusion of water vapor molecules. Downpour™ hydrophilic membranes have a solid structure that physically stops water passing through the membrane. The chemical structure of the membrane is made up of hydrophilic (water loving) groups that attract water vapor molecules. Driven by greater heat and water vapor density, the water vapor molecules move from one hydrophilic group to the next (somewhat like stepping stones).