How comfortable a blanket is partly depends, of course, on how well-suited it is to the environment it's in. Freezing air makes a thick blanket comfortable. But inherently on three properties:
a) Thermal insulance. How good the blanket is at resisting heat flow. Mostly, this insulating quality is due to air trapped between the fibers, not to how conductive the fibers themselves are. This property is measured in togs, or more recently in Rtc. (Standard ISO 11092).
b) Resistance to air flow. A wind blowing through a blanket is chilling. (Standard ISO 9237) But:
c) Permeability. Ability to permit moisture (humidity) to escape. People constantly give off moisture. If you have ever spent a night in an aluminized mylar "survivor" or "space blanket", you know how important this property is.
International aid agencies buy tens of thousands of blankets annually for refugees, and they specify the blankets' properties. The major agencies (Red Cross, Red Crescent, UNHCR and UNICEF) have standardized on three types, all 1.5 by 2 meters (59 by 79 inches):
• Medium thermal type, with a TOG of 2.5, is the minimum for hot or temperate climates (even in hot countries, nights can be cold).
• High thermal type, with a TOG of 4, is appropriate for cold climates.
• A blanket with TOG 1.5 is appropriate for indoor use, on a bed, in a house with heating facilities. Outdoors in most climates, or even indoors without a heater, a blanket with a TOG 2.5 is the minimum.
Scientific studies defined that indoors at 20°C, a person at rest requires a total insulation of TOG 1.5. Outdoors with no wind the value at 10°C is TOG 4, at 0°C it is TOG 6, at -10°C it is TOG 8 and at -20°C it is TOG 9.5. Bearing in mind that a part of the insulation comes from the clothing, the rest will come from the blanket.
Around 2016 the agencies switched from togs to Rtc