What Is the Warmest Fabric Used in Blankets?

How Blankets Work

• A practicing musician is likely to tell you that the notes he plays are only one component of the music you hear. The other major component is the space between the notes, which determines the rhythm and overall character of the notes. A warm blanket works rather like a piece of music. Warmth comes not just from fabric threads that shields you from external cold and air movement. Warmth also comes from the spaces between the threads which store warm air generated by body heat and keep it close to the body. A critical element in the warming capacity of a blanket is the ability of the fabric to hold warm air. Blankets used in many hospitals may be made of cotton, to tolerate frequent bleaching, but are woven with air pockets in the weave, to make them hold more warm air.

How Fabrics Hold Air

• For keeping cold air away from the body, one effective quality a fabric can have is a very tight weave. Sleeping bags, ski parkas and camping tents all use a very finely woven fabric like nylon to shield the body from cold ground and wind. Very tightly woven fabrics have the further advantage of keeping out moisture. What they do not do, however, is provide any insulating layer of air between the cold and the body. Worse, in addition to keeping moisture away from the skin, they force the skin to retain its own moisture. Parkas and sleeping bags add a layer of fuzzy filling, synthetic or natural, which improves heat retention but still does not allow body moisture to dissipate. Buying a quilt or duvet made from a natural fabric like cotton and filled with synthetic or natural feather down combines a fabric that absorbs and allows for evaporation of body moisture with a substance full of warm air-holding spaces. Achieving both these goals with a single sheet of fabric is a greater challenge.

Blanket Fibers

• Wool fiber is the model for manufactured blanket fibers like nylon, acrylic and synthetic polar fleece. Wool possesses a crimp that means fibers in even the most tightly woven wool yarns do not lie completely flat against each other. Relentlessly curly or kinky, they retain spaces that hold warmth, making wool a leader in warmth. Nylon, acrylic and other synthetic yarns imitate the fuzzy loft of woolen fibers, but their chemical bases make them poor wicks for body moisture. The only successful synthetic rival to wool in warmth retention is synthetic polar fleece. Polar fleece possesses the capacity to wick away body moisture while holding heat in its many tiny air pockets. For those who are allergic to wool, fleece provides an alternative fabric with similar warming characteristics.

The Warmth Paradox

• Ultimately, as any two people who share a thermostat will tell you, warmth is a very subjective sensation. The British TOG rating of thermal resistance was developed to describe warmth in quantitative terms. In the U.K., duvets and especially bedding for children are often TOG rated. In the U.S., however, blanket warmth is still determined one sleeper at a time. There are several important factors to consider when shopping for a warm blanket. Wool and polar fleece both excel in wicking away body moisture while trapping warm air. Weight alone does not determine the warmth of a blanket. In fact, some very heavy blankets may have such compressed fibers that they hold little warm air. Natural fabrics let body moisture escape better than synthetic ones. The heat-retention qualities of any blanket can be improved by covering it, rather than the sleeper, with a sheet or other fabric of fairly tight weave.