|David J Heffer and Associates|
|CONSULTING TEXTILE TECHNOLOGISTS|
DOWN AND FEATHER TESTING
We have many years experience in the analysis of down and feather products. Commonly used tests include:
Composition of Filling
Suppliers and retailers of down and feather filled products, including sleeping bags and quilts, can avoid the misleading or deceptive description of down and feather filled products by conducting regular checks on the composition of the filling. It is not sufficient to rely on the results provided by the supplier. In Australia, claims of 100% down can no longer be made. Further, the amount of down clusters in a filling must not be less than the nominal down content, i.e. the down content must not include any tolerance for components such as down fibre.
Any discussion of quilts or sleeping bags will invariably include a reference to the ‘warmth’ of the product. Thermal resistance is a measure of the resistance of a material to heat flow. A product that has a high thermal resistance will provide better insulation between a sleeping body and the environment in which they sleep. A person who describes themselves as a ‘cold’ person generally means that they prefer a quilt with a high thermal resistance if they are to remain comfortably warm through the night. A person who sleeps ‘hot’ requires a quilt with a lower thermal resistance to be equally comfortable.
The thermal resistance of a quilt or sleeping bag is measured in togs. One tog equals 0.1C/m2/W. The name ‘tog’ is derived from the old English slang for clothing. It is not an acronym as is commonly thought. The tog is the unit for thermal resistance just as the kilogram is the unit for mass.
Thermal resistance - typical values
Quilts of various types in the Australian market would generally fall within the range of 4-12 tog. Typically, a lightweight polyester quilt would represent the lower end of this range while high-down content quilts would be found at the top end of the thermal resistance range. It should be noted that any filling can be used to deliver any desired thermal resistance value. By adjusting the amount of the filling in a quilt the thermal resistance will be altered. Thus, a quilt filled with shredded paper could be made to have a thermal resistance of 15 tog. In other words, the thermal resistance should be understood as a performance characteristic and not as a quality characteristic.
The most common thermal resistance values for double and queen sized quilts in the southern states of Australia would fall in the range 7-9 tog.
Individual requirements for thermal insulation
It should be understood that each person has their own individual requirements for thermal insulation. It is a common experience that children sleep ‘warmer’ than adults. Men often report needing less bed covering (i.e. less insulation) than women. The thermal insulation depends on many factors including age, sex, state of health, level of activity and the time since the last food intake. Thus, a person requires an appropriate level of thermal insulation to maintain thermal comfort. For one person this may mean much less insulation than required by another. It is inappropriate to select bedding because it has the highest thermal resistance.
Warmth to weight ratio
The warmth to weight ratio provides a measure of the weight required to produce a particular thermal resistance. Blankets have a relatively low warmth to weight ratio. Quilts provide more insulation for the same weight. Typically, wool filled quilts have warmth to weight ratios ranging from 90-120. Polyester filled quilts (carded batt type) fall within the range of 110-140. Feather and down filled quilts generally range from 120-160. A high warmth to weight ratio indicates that the quilt is relatively light for the particular thermal resistance.
Some people like the security associated with relatively heavy bed covering. They should look for lower warmth to weight ratios. Others may require a high thermal resistance but feel tired if they sleep under a heavy quilt. They should look for a high warmth to weight ratio.
Again, it is inappropriate to take the simplistic view that a high warmth to weight ratio is desirable for all consumers..