Most materials have been measured to determine how much heat energy moves through them for a STANDARD size of material. This number is typically referred to as the Conductivity or W/m K for the material. (cal/sec)/(cm2 C/cm) and BTU in /hrft2F simple conversions of W/m K to represent Conductivity.
Thermal Resistance is the inverse of Conductivity. 1/C = R. If you want to know how much insulation your jacket or quilt/sleeping bag provides, you look up the Conductivity value, take the inverse, and then adjust the standard thickness for the CUSTOM thickness of the item you want. The scientific community uses m2K/W as the standard thermal resistance number. R-Value, clo, and TOG are simple conversions of the m2K/W number.
Most of the answers, to insulation related questions posted to this forum, require a moderate understanding of human physiology, thermo dynamics, and thermal testing methodology. I studied these disciplines in support of a start-up venture I am dabbling in. Related to that venture, I personally thermal tested many of the products that are discussed on this forum. Roger Caffin is also quite knowledgeable in the above fields and we are fortunate to have him as our moderator.
My summary advice is that you can ignore all of the technical stuff posted by me and others and still make excellent sleep system consumer decisions. Do this by looking at the EN 13537 test results for a particular product or one that is similar in construction to a tested model.