SATRA STM 175 Permeability and absorption test machine
This is a preferred SATRA test and unlike many other methods it attempts to simulate the environment within a shoe, that is 100% relative humidity at foot temperature.
As well as measuring the amount of moisture transmitted through the material, the quantity of moisture absorbed by the upper can also be determined. This is important because although some materials may be impermeable, the ability to absorb moisture means that the foot will feel dry to the wearer. The moisture can desorb from the material by evaporation once the shoe is off the foot, for example, overnight.
An assembly of discs of outer material, lining (if used in the footwear) and a standard hose (sock) fabric is clamped and sealed across the top of a plastic pot containing distilled water. The water inside the pot is maintained at a temperature of 32°C by resting the pot in a temperaturecontrolled water bath. The atmosphere outside the pot is maintained by carrying out the test in a conditioned room and maintaining a flow of air across the top of the pot at a speed equivalent to a brisk walking pace. If the outer is permeable, water vapour passes through the cotton hose and the test material in the same way that perspiration would in a shoe.
The permeability of the material is determined by measuring the weight loss of the assembly at intervals throughout a six-hour period. Care is needed during the test to avoid splashing the reverse of the test sample with the water inside the pot and to ensure that the outer surface of the test pot is thoroughly dried after it is removed from the water bath for weighing. The absorption of the upper material, lining and the standard cotton hose are measured by weighing each disc at the start and end of test.