Multi-layer composite yarns and textiles have other physical possibilities for achieving wear comfort in terms of absorbing sweat released from the human skin surface by an internal sweat absorbent layer. Toyobo Co. Japan developed a cool and dry three layer composite yarn, which consists of a polyester filament yarn on the surface, a staple polyester yarn in the middle and a polyester filament yarn in the core. The finest components lying in the middle, i.e. fine fibers offer greater porosity, which increases capillary action, conveying the absorbed sweat to the yarn surface. The coarse polyester filament yarn in the yarn interior has a Y-shaped cross section in order to increase moisture absorption capacity.

Insulation

The required thermal insulation of clothing systems primarily depends on the physical activity and on the surrounding conditions, such as temperature and relative humidity. The quantity of heat produced by humans depends to a large extent on the physical activity and can vary from 100W while resting to over 1000W during maximum physical performance.

In cooler seasons, for example when ambient temperature is approx. 0C, thermally insulated clothing is recommended in order to ensure that the body is sufficiently warm when resting. If, however, the body is involved in a more intensive activity (as in case of winter sports), the body temperature increases with enhanced heat production. To keep this increase within limits, the body perspires in order to withdraw energy from the body by evaporative cooling. If the thermal insulation of the clothing is reduced during physical activity, a part of the produced heat can be removed by convection and the body will not be required to perspire so much.

The quality of insulation in a garment will be extensively governed by the thickness and density of its component fabrics. While high thickness improves insulation, a garment made from a thick fabric will have greater weight impairing the freedom of movement of the wearer. Thus low density is also important for improving insulation. In many practical examples, thermal insulation is provided by air gaps between the garment layers. The external temperatures also affect the effectiveness of the insulation. The more extreme the temperature, be it very high or very low, the less effective the insulation becomes. Thus, a garment designed for its ability to protect against heat or cold is selected by its wearer on the expectation of the climate in which the garment is to be worn.

Clearly there is a need for garments made from intelligent fabrics that can provide superior protection as well as wear comfort. A number of intelligent materials and textiles are available today.

a)      Phase change materials

When a material changes phase with increasing temperature, e.g. from solid to liquid state, a large quantity of latent heat is absorbed. This input of heat is necessary to transform the solid material to the liquid state, and the change will occur at an almost fixed temperature-the melting point of the material. The heat is, in effect, stored in the material in its liquid state and is only released when the liquid is cooled back to its solid state. This behavior forms the basis of phase change materials.