The so-called fabric breathability refers to the performance of the fabric through the air under the condition of pressure difference on both sides of the fabric. That is, the air volume of the fabric unit area in unit time is L/mm2s under the specified pressure difference. Because the pressure difference is the necessary condition for the air to flow, it is only necessary to maintain a certain pressure difference on the two sides of the fabric to produce air flow in the fabric.
Factors affecting the permeability of fabrics:
(1) fabric structure:
When the compactness of the fabric stays the same, the permeability of the fabric decreases with the increase of the arrangement density of warp yarn and the increase of yarn density. In a certain range, the twist of the yarn increases, the diameter and compactness of the yarn decrease, and the permeability of the fabric increases. In terms of fabric tissue, in the same arrangement density and compactness, the air permeability is ordered to be plain weave. The larger the volume fraction, the worse the permeability.
(2) fiber properties and yarn structure:
The moisture regain of fiber has obvious influence on air permeability. If the wool fabric increases with the moisture regain, the permeability decreases significantly, which is due to the radial expansion of the fiber. Most of the fiber fabrics have better air permeability than circular section fiber fabrics. The shape of the fiber surface and the shape of the section will increase the resistance of air flow due to the obstruction of the form and the increase of the surface machine. Therefore, the shorter the fiber, the greater the rigidity, the greater the probability of the product feathers, the more the blocking and channel changes formed, the worse the air permeability.
The closer the structure of the yarn, the smaller the inside of the yarn, and the greater the penetration between the yarns. The twist of the yarn is good for transparency.
(3) the environmental conditions:
When at a certain temperature, breathable fabric quantity along with the increase of relative humidity is on the decline. This is due to the hygroscopic and expansion of fiber reduce fabric interior space, can jam and part of the water channel.
When the relative humidity, the amount of breathable fabric increases with the rising of temperature with the environment. Because when the environment temperature, on the one hand, make the gas molecular thermal motion increases, lead to molecular diffusion, enhanced ability to break through. Fabric overall thermal expansion on the other hand, make the fabric through improved connectivity.
When at constant temperature and relative humidity, fabric on both sides of the change of pressure difference will affect the ventilation rate of fabric, and is non-linear. Because of the pressure difference, the greater the pore air velocity through the fabric faster, produced by the air resistance, the greater the hand will cause the bending deformation of fabric, elongation, increase the hole, on the other hand - compression fiber aggregation state and arrangement, lead to holes, and fabric density increase. Both impact on ventilation rate is on the contrary, therefore in the process of practical measurement shall determine a small pressure difference interference, as the constant test conditions.
