The Men's Fast Alpine Stretch Neo Jacket is so breathable it blurs the line between "hard" and "soft" shell and can comfortably be worn continuously during heavy athletic exertion, such as ice climbing or ski mountaineering. Ventilation membrane is the “original” idea for keeping a fabric more breathable. The mechanism behind this technology is based on having a good balance between “straight” pores that allow air to flow into the garment and angled pores that block the wind. The more straight pores there are, the more air can flow into the waterproof clothing – but then there is also a higher chance of water “slipping” in. For instance, Polartec claims that the Neoshell is 97% windproof, but that comes with a waterproof level of 10,000mm hydrostatic head.
Ventilated fabrics are really useful when less rain is expected and you are going to be doing a higher impact activity. Many times waterproof clothing using this technology will be considered softshells rather than the traditional hard shells and will be sold as a more active use garment.