Vapour-pressure deficit temperature, the relative humidity and, if possible, the canopy air temperature. We must then compute the saturation pressure. Saturation pressure can be looked up in a psychrometric chart or derived from the Arrhenius equation, a way to compute it directly from temperature is where: To convert between Rankine and degrees Fahrenheit: formula_10 We compute this pressure for both the ambient and canopy temperatures. We then can compute the actual partial pressure of the water vapour in the air by multiplying by the relative humidity [%]: and finally VPD using formula_12 or formula_13 when the canopy temperature is known. Vapour-pressure deficit
SympaTex common polyurethane equivalent, it can also be referred to as a monolithic membrane. No water can get in from the outside, but water vapour molecules are transported through the membrane from the inside to the outside by way of an absorption and evaporation process. This moisture transfer through the membrane is what is referred to as "breatheability." A closed membrane like SympaTex differs from microporous membranes (such as Gore-Tex) which have microscopic pores that let air (and water vapour) pass through, yet have such low surface energy that the surface tension of any (liquid) water in contact remains too high