Are layers really warmer?

December 20, 2006 6:10 AM

If layers are better for warmth (as I have been told as long as I can remember), why isn't there a blanket made out of a bunch of thin layers fastened together?
posted by white light to grab bag (19 comments total)

Quilts. Two layers of fabric with filling. The quilting makes pockets that stay warm.
posted by saffry at 6:11 AM on December 20, 2006

Layer are better because you can do different things with them.

Layer next to skin designed to wick away moisture (eg merino underwear)

Mid-layer to trap air, as insulation (eg Polartec fleece)

Outer layer to stop wind and water but allow water vapour to pass through on the way out (eg Goretex).

Some clothing has all three layers fastened together but if you keep them separate you can mix and match for different conditions (eg on a dry day you don't need a waterproof outerlayer so you can use a more breathable but still windproof layer). Also if a particular layer gets wet you can swap it out while keeping the others in use.

Blankets were traditionally used indoors as a mid-layer between a sheet (inner layer) and a counterpane (outer layer).
posted by unSane at 6:23 AM on December 20, 2006

I think you may be confusing "better for warmth" with "better for working/being outside". It's my understanding that what keeps a person warm is simply putting as much insulation between him/herself and the outside as possible. The more space/insulation the better. The only reason you'd want layers is to remove one or two if you're exerting yourself and sweating. "Dressing like an onion" allows you to more precisely adjust the insulation between you and the outside to keep you from sweating through and subsequently freezing. When a person is in bed, he/she not (usually) exerting him/herself and so removing a layer isn't a real necessity.
posted by cog_nate at 6:24 AM on December 20, 2006

Layers are better for a couple of reasons. First, warmth is trapped between layers, and second, because it offers unparalleled flexibility. Too warm? Just strip a layer and keep going. A layer got wet from perspiration, just replace that one layer and keep going.

The second isn't super-relevant for a blanket, and the first - that the structure of layers has thermal properties - is taken care of by the structure of a blanket or other bedcovering itself. The way down feathers leave air pockets when bunched up achieves the same effect. Same thing with synthetic batting or even just the weave of a wool blanket.

Where I live I think most people do use layers to sleep - usually a top sheet, a duvet, and some kind of wool or fleece blanket on top of that, at least over the foot half of the bed.
posted by mikel at 6:28 AM on December 20, 2006

2nd what cog_nate said -- beat me to it =D
posted by vanoakenfold at 6:39 AM on December 20, 2006

A filled duvet (in the American sense of 'comforter cover') gets you pretty much what you're describing.
posted by kimota at 7:07 AM on December 20, 2006

And if some huge percentage of your heat escapes through your head, why can't we develop a hat that allows us to walk around otherwise naked?
posted by bendybendy at 7:13 AM on December 20, 2006

Because your body gives top priority to keeping your head and torso at a constant temperature. Not so much for your extremities.
posted by DevilsAdvocate at 7:25 AM on December 20, 2006

bendybendy - a huge percentage of heat escapes through the head because people don't like to wear hats. If people only wore hats, then the vast majority of heat would escape through the body.
posted by Void_Ptr at 7:27 AM on December 20, 2006

The blankets ARE the layers.
posted by Thorzdad at 7:29 AM on December 20, 2006

Here's the science:

Layers are good at keeping you warm because they slow down the rate at which you lose heat. Air (trapped between the layers) is a very good insulator - it does not conduct very well and if it is trapped (i.e. stationary) then it is difficult for convection currents to be set up.

If you had a blanket made of lots of layers all on top of each other then the collective weight of the layers would collapse any air gaps, thereby reducing the blanket's insulating ability.
posted by alby at 7:40 AM on December 20, 2006

bendybendy - a huge percentage of heat escapes through the head because people don't like to wear hats. If people only wore hats, then the vast majority of heat would escape through the body.

Heat escapes more rapidly through your head than your torso. Go ask the Red Cross.
posted by Mikey-San at 8:01 AM on December 20, 2006

My best blanket is an old army blanket that I covered in layers of flannel. The wool makes it heavy, the flannel makes it soft and better insulated. Perfection.
posted by Sara Anne at 8:15 AM on December 20, 2006

alby have the right answer : layers are warmer if they allow stationary air between them. If they don't, they're useless.
posted by racingjs at 8:23 AM on December 20, 2006

Also seconding alby - layers do not "trap heat", they trap air, and air is a good insulator (see also: double glazing).
posted by EndsOfInvention at 9:04 AM on December 20, 2006

The filling in quilts and such is basically the same as layers, it is composed of many little air pockets that (like most insulation) slows down the loss of heat through convection (which requires the free flow of air to work efficiently).
posted by nanojath at 9:27 AM on December 20, 2006

I've always been a fan of layers because if you start to sweat, you can take a layer off instead of having the sweat freeze and make you colder. It helps with the crazy weather we have here in New England!
posted by deansfurniture5 at 1:18 PM on December 20, 2006

Isn't the wool or other fabric a blanket is made out of the same as ten thousand randomly distributed layers with ten thousand randomly distributed air pockets between them?

In other words, a blanket uses layers, on a micro level.
posted by AmbroseChapel at 5:04 PM on December 20, 2006

A lot of heat escapes from your head for several reasons:

1. The situation is most often encountered when you are wearing lots of warm clothes but no hat... go figure.

2. The head is at the top of the body... heat rises...

3. Your brain uses a surprising amount of the body's energy output

4. There is no insulating layer of fat around your skull

There are probably other reasons too.
posted by unSane at 7:17 AM on December 21, 2006