Page "Thermal insulation" Paragraph 32

Industry standards are often rules of thumb, developed over many years, that offset many conflicting goals: what people will pay for, manufacturing cost, local climate, traditional building practices, and varying standards of comfort.

Both heat transfer and layer analysis may be performed in large industrial applications, but in household situations ( appliances and building insulation ), air tightness is the key in reducing heat transfer due to air leakage ( forced or natural convection ).

Once air tightness is achieved, it has often been sufficient to choose the thickness of the insulating layer based on rules of thumb.

Diminishing returns are achieved with each successive doubling of the insulating layer.