Why do people get so hung up about thermal insulation, it really is not difficult.   The main thing to remember is that the power, in watts (W, J.s-1) that passes though a material is approximately proportional to three things, conductivity (k, λ), temperature difference (∆T) in kelvin (K), and thickness in metres (m). In arithmetic terms, the thermal conductivity of a material is written as W.m-1.K-1, or W/m.K (as I have never found a way to write a superscript negative sign on m