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Breathability is the ability of a fabric to allow moisture vapor to be transmitted through the material. ==Mechanism== Air Permeability is the ability of a fabric to allow air to pass through it. While Air Permeable fabrics tend to have relatively high moisture vapor transmission, it is not necessary to be Air Permeable to be breathable. Moisture Vapor Transfer (MVT) in waterproof fabrics occurs by two processes: * Physical: Hydrophobic (water fearing) are water proof, yet steam permeable -microporous coatings or laminations have pores that are so small that liquid water cannot go through. However, vapor water molecules are many times smaller than the liquid state and can pass through these “micro pores”. * Chemical: Hydrophilic (water loving) / non-porous lamination or coating move moisture by chemical diffusion. The water molecule is positively charged and the hydrophilic PU is negatively charged, attracting the water through the intermolecular gaps of the PU. Because the ionic bond is relatively weak, the water then gets pushed through the gaps until the water vapor passes all the way through. Driving Force is the difference in the level of heat and humidity on one side of the material compared to the other side. Also known as the Differential Pressure. By 2nd law of thermodynamics moisture will move towards dry. Therefore, warm, moist air will flow towards cold, dry air until there is an equilibrium. Due to body heat and moisture there is almost always higher heat and humidity inside a clothing system. This creates a differential pressure forcing the heat and humidity toward the outside. The greater the difference between the heat and humidity inside the clothing system and the outside, the greater the Differential Pressure to push that heat and humidity out. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「breathability」の詳細全文を読む スポンサード リンク
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