How Much Blanket Is Enough: A Tog Sizing Rule from Sleeping Heat Production, Room Temperature, and the Insulation Already Supplied by the Mattress

Bedding is rated in tog, but the rating a sleeper needs depends on the room, and the common advice to buy the heaviest winter duvet overshoots for most heated bedrooms. This paper balances a stated heat flux of 12 W per square metre through the upper bedding against conduction through the bedding stack, and computes the blanket insulation required from 10 to 25 degrees Celsius. The requirement falls from 15.5 tog at 10 degrees to 8.0 tog at 19 degrees and 5.5 tog at 22 degrees. A 13.5 tog duvet in a 19 degree room therefore carries 5.5 tog of surplus insulation, which in the model would drive mean skin temperature to 40.1 degrees if the sleeper did not respond by throwing it off. The sizing rule is one subtraction per degree of room temperature, tabulated in full. This study is simulated, not measured.