Wool Insulation - Insulating Qualities

Insulating Qualities

Sheep wool is a natural insulator because it has a crimped nature which traps air in millions of tiny pockets. Air is an excellent insulator since it does not conduct or disperse heat well. Sheep wool insulation has an R-value (resistance to heat flow) of approximately 3.5 to 3.8 per inch of material thickness which is 0.3 to 0.6 points higher than some glasswool, cellulose, and some mineral wool. The crimp also allows the wool to retain its structure and overall thickness instead of breaking down and settling like many other insulating materials. Wool is a hygroscopic material which means that it is thought to absorb up to 30% to 40% of its own weight in moisture without becoming wet to the touch. This is also claimed as a performance benefit by many wool insulation manufacturers but the attribute remains unproven in building applications. This moisture absorption is unique to sheep wool and does not compromise the wool's insulating abilities unlike cellulose or fiberglass insulation. When used as acoustic insulation wool provides rates starting at 44 dB for a 60 mm (2.4 in) thick partition, and goes up to 53 dB for a 100 mm (4 in) thickness. Wool has a long life span and can be used over and over again. Wool also has a low manufacturing energy at approximately 15 megajoules per kg of material produced. The low manufacturing energy of wool is just over half of that of cellulose insulation and practically one sixth of the manufacturing energy required to produce mineral wool, however, if one takes into account the embodied energy of the whole lifecycle, the use of recyceld polyester in the product has reduced the embodied energy. The issues of transportation energy costs need to be factored in, as the embodied energy figures usually do not consider this. Consumers must think about both transportation stages, pre-production, as a raw material, and post-production as insulation, to be careful to choose a manufacturer that is as close as possible to the building site.