By P Sudhakar and V R Sam Path
Department of Textile Technology, K S Rangasamy College of Technology,
Tiruchengode 637 209, Tamil Nadu

Breathable fabrics constitute one of the major components of individual protective clothing used in high altitude conditions. Membranes have opened up entirely new possibilities for designing functional clothing.

Woven or knitted fabric can have desired properties such as insulation and fashion. Often these properties are not enough for daily-use in bad weather conditions. The rain proofness of the fabric has to be increased. This can be done by applying PVC, acrylics, silicones, polyurethanes or fluorocarbons to the fabric. However, by doing so, the fabric is sealed: water form outer-environment (rain, snow etc.) can not pass and sweat as water-vapour can not be eliminated through the fabric. This situation will cause condensation in the garment and, thus, a general state of discomfort.

Breathable fabrics constitute one of the major components of individual protective clothing used in High altitude conditions. The technical excellence and comfort aspects of these fabrics have enhanced the combat efficiency of the army personnel working under severe conditions of extreme cold weather. Fabrics having water proofness, wind proofness and water vapour permeable characteristics are commonly referred as breathable fabrics. In this paper the technology of manufacturing breathable fabrics, garments, their suitability and their properties are discussed and reviewed.

Thermo physiological comfort is a complex phenomenon and relates to the thermodynamics, heat and moisture transfer of the human body and clothing. The heat balance of the system is a function of skin, clothing and amount of air entrapped between skin and clothing. This heat balance varies with the change in wind velocity, atmospheric temperature (external factor) or the activity of the individual (internal factor) causing change in heat or moisture production of the body. The individual will feel comfortable till the amount of heat produced is equal to the amount of heat lost.

The advent of polyurethane/PTFE coating offered to the textile technologist to design and engineer comfortable water proof clothing as an alternate to PVC. The ultra light polyurethane coated fabrics eliminate the common problems experienced in PVC clothing that include poor flex properties, abrasion resistance and low temperature ageing properties. Compared to its counterparts, polyurethane coated fabrics are flexible, abrasion resistant, light weight, possess good cold ageing properties and some of the grades are even breathable. In addition to the above, special grades of PO offer excellent drape properties, softness and suppleness of hand and could be processed to exhibit high gloss and transparent properties.

In quantitative terms a breathable fabric should have the following characteristics

. Water vapour permeability 3000 g/m2 24 hr
. Water proofness min. 130 cm, hydrostatic pressure.
. Wind proofness-less than 1. 5 m!, cm2/ sec at 1 m bar,
. The fundamental considerations that need to be considered while designing a breathable fabric for high attitude conditions include,
. Water proofness
. Mass of the fabric
. Durability/flexibility of coating/ laminating
. Comfort level
. Camouflage effect to deceive the enemy and match the UV reflectance of snow/mountains.
. Aesthetic property
. Water vapour transmission
. Effective clothing against wind chill factor.

Water resistant breathable fabrics

To avoid the condensation of perspiration in a garment, it has to be made with breathable fabrics through which water-vapour can escape. In general there are three different ways to create - water resistant but breathable fabrics.