Heat Transfer
Rate of heat transfer through a textile material determines its performance in temperature-regulating apparel and home furnishings. The thermal conductivity of linen fabric is high compared to other natural fibers, because flax fibers possess a highly crystalline molecular structure and a dense physical packing. This property allows heat to escape rapidly from the body of the wearer.
Consequently, linen garments provide a cooling effect that is highly valued in warm climates.
Fiber Structure
Physical density and moisture regain of bast fibers are the main variables that control the transmission of heat through the finished cloth. The high thermal conductivity of flax is enhanced by the presence of a central lumen in each elementary fiber, which conducts moisture and heat away from the skin. When linen fabric absorbs perspiration, the water further increases the heat transfer rate, because water conducts heat much faster than still air.
Laboratory testing of the fabric uses a hot-plate apparatus to measure the thermal resistance of different fabric densities. This testing demonstrates that open structures with high air permeability maintain a lower thermal resistance than dense, tightly constructed fabrics.
Fabric Finishing
Finishing treatments such as calendering or brushing alter the surface texture and bulk of the linen fabric, which modifies its warmth. Calendering flattens the yarns and increases contact area, which enhances the rate of heat dissipation. In contrast, brushing creates a raised surface that traps air, which lowers the heat transfer rate.
