Why is my jacket warm?

[shortbow]

I was out for a walk today. The temperature was in the high thirties. I was wearing an A shirt, t shirt, light cotton dress shirt and my 1990 Cooper G1. I was warm.

What is it about goat skin that accomplishes this feat without any insulation? I was rather pleasantly surprised and somewhat mystified. Of course, the mouton collar helps a lot. But still, that's a pretty thin material, which if made of some fabric would have left me quite uncomfortable. What don't I know?

 

[DavidVillaJr]

Isn't it that leather is a smooth "uniform" surface without holes, whereas fabric of any source is woven together from "thread" and so has more areas for air to squeeze through?

dv

 

[Tomasso]

Isn't it that leather is a smooth "uniform" surface without holes, whereas fabric of any source is woven together from "thread" and so has more areas for air to squeeze through?

Bingo!

 

[Baron Kurtz]

Well that actually sounds counter-intuitive. A woven fabric should generate a layer of air between the inside and outside of the fabric, an insulating layer; Like double glazed windows. A leather jacket does not do this. This is the explanation, I thought, for the common observation that thinly lined leather jackets are almost always less insulating than woolen alternatives, and also part of the explanation why woven animal hair became so popular as a covering.

A proper experiment would have been to change into a wool jacket of a similar cut with a fur collar. But I suspect that the apparent warmth was due to other reasons than the leather.

bk

 

[carldelo]

Well that actually sounds counter-intuitive. A woven fabric should generate a layer of air between the inside and outside of the fabric, an insulating layer; Like double glazed windows. A leather jacket does not do this. This is the explanation, I thought, for the common observation that thinly lined leather jackets are almost always less insulating than woolen alternatives, and also part of the explanation why woven animal hair became so popular as a covering.

A proper experiment would have been to change into a wool jacket of a similar cut with a fur collar. But I suspect that the apparent warmth was due to other reasons than the leather.

bk

A double-glazed window insulates because the air within is prevented from mingling with either the interior or exterior air. The heat transfer therefore happens through 3 layers, glass-air-glass. If the outer or inner glass were porous like fabric, it would not insulate as well, as the escaping air would take thermal energy with it.

A woven fabric can utilize this effect only to the extent that the incorporated air layer is thick enough to constitute a significant barrier to heat transfer, and that it not be very porous. Thick, heavy wool will do this, but not thin, unless it is less porous. I agree that thinly-lined leather jackets don't insulate well, and I think it is probably because there isn't much of an air layer trapped between the leather and the lining. Flannel lined or quilted jackets are obviously warmer - the lining is such that a thick layer of air is trapped within.

To me it seems the leather jacket is working well because it is holding the air inside the jacket completely, with the aid of the fuzzy collar as a seal at the neck, and I presume some sort of stretchy waistband material. The presence of several layers under the jacket helps also. In order to escape, the heat from the wearer has to transmit through each fabric layer, plus the layers of air between them. That's why layering works - to work best, fabric layers should be somewhat loose, to allow for the presence of a thick air layer, and restrict air movement between layers. As a bonus, if the fabric allows water vapor to leave through its pores, without allowing much air to go through, then you have wicking fabric that helps keep the inside comfortable. This is why silk, thin wool and polypro are good insulating layers, and why looser is generally better in cold-weather outerwear.

I have noticed that smooth leather jackets are not as good as fuzzy wool coats in high winds. I believe this is because convective heat loss is enhanced at the smooth surface - on a fuzzy jacket, the air boundary layer will be thicker, with a gentler velocity gradient that mitigates heat loss. Basically, the fuzziness slows down the average velocity of the wind near the jacket surface, reducing convective heat losses.

 

[Peacoat]

I have found goat jackets to be the coldest, with horse being the warmest, and cow (or steer) about in the middle, maybe a little closer to the horse in warmth. But the difference isn't much, and we don't wear leather jackets for their warmth. It is what we insulate with under the leather shell that gives the warmth. Most leather jackets will do a good job of keeping the wind out, and properly treated, will do a good job of keeping the rain out, but they don't keep us warm by themselves.

When it gets cold, I go with a peacoat, and if it is really cold, I wear a sweater under the peacoat. Keeps me warmer than any of my leather jackets.

I think Shortbow gave the clue to the answer to his question in the first sentence of his post. He said he was ". . . out walking today . . . ." The walking generated enough heat to properly warm his body, and to warm the air trapped inside the shell of the jacket, thus keeping him warm longer.

 

[Yeps]

I think Shortbow gave the clue to the answer to his question in the first sentence of his post. He said he was ". . . out walking today . . . ." The walking generated enough heat to properly warm his body, and to warm the air trapped inside the shell of the jacket, thus keeping him warm longer.

That was my first thought as well.

I was wearing an A shirt, t shirt, light cotton dress shirt and my 1990 Cooper G1. I was warm.

Also, never underestimate the insulating power of a few thin layers. The two undershirts probably actually had quite a bit to do with it.

 

[Tomasso]

Also, never underestimate the insulating power of a few thin layers. The two undershirts probably actually had quite a bit to do with it.

Yes, with the leather jacket acting as a shell or windbreaker. That said, leather as a shell does not perform particularly well in low temps as it lacks the breathability and flexabilty of modern microfibers.

 

[Mr Badger]

Yes, with the leather jacket acting as a shell or windbreaker. That said, leather as a shell does not perform particularly well in low temps as it lacks the breathability and flexabilty of modern microfibers.

But it looks a HELL of a lot better!

I reckon Peacoat's nailed it. I walk to work and back each day and, even on the journey into town, the combination of a temp change of around 5C as the buildings get closer together and brisk motorvatin' on the old plates has been making my goat Aero A2 and a shirt more than a little overly-warm by the time I hit my desk. However, standing around waiting for a bus in the same temps, it's not warm enuff!

I have used the combo of a G1, five-button wool army sweater, cotton tee and silk scarf while walking to work in just sub-zero temps without feeling cold, so I think Yeps is right about the layering, too...

 

[shortbow]

Thanks everyone, lots to think about. In response, I have to say that I've spent inordinate numbers of hours out of doors in all kinds of weather and have mostly relied on wool and some sort of windbreaker until it gets seriously below zero, then out comes the down. I have lots of wool and I know none of it, on it's own, weight notwithstanding, would have performed as well as the G1. In addition to and in support of some of the thinking above mentioned I think it may have much to do with the fact that with the tight sleeves, waist and neck, the exercize induced warmth was not allowed to escape at all. Neither did I perspire. Still, I noticed that even when holding the leather against the skin of my forearm I felt no sensation of cold, which to borrow a word from one of you, also seems counter-intuitive. An interesting question to exercise a few brain cells on, anyway.

 

[Richard Warren]

It was probably your hat that kept you warm.

 

[bumphrey hogart]

It was probably your hat that kept you warm.

Yes,the old saying 'if you've got cold feet put on a hat' is as true today as it's ever been.
I also sometimes wonder if there is a quality to 'good leather we don't get.I take it leather was used in the past as a windproof,waterproof outer layer because it was the better than the alternatives,why else would the army/air force issue it otherwise?(obviously abrasion resistance played a part too).
Then with the advent of modern materials like nylon etc,leather became largely obsolete apart from it's 'fashion' application.(When I went to do my basic motorbike training,I was told to take off my thick schott leather and was given some hi-tec nylon jacket to wear instead).There are still some obvious advantages,I was helping with the village fire for bonfire night a couple of days ago, and with the sparks flying I know I was far better off with my leather than my mate was with his 'goretex',but is there a quality in leather,when it warms up with your body heat and is sufficiently thick,that makes it superior to the more modern fabrics in certain circumstances?
I know if I was out on a windswept moor,with the rain coming at me horizontally I would far rather be in my modern coat,but why then when it's damp,cold and miserable and I'm walking the dog a couple of miles down the local trail do I reach for my leather?There's just something so much more comforting and comfortable about it,and yet the modern stuff is 'so patently superior'.
Have we missed something about the property of hide?

 

[Foofoogal]

I just cannot imagine Harley riders wearing Nylon.
lol

 

[Peacoat]

We don't, unless it is hot out and we want some protection from the road in the event of a go down.

 

[shortbow]

I still think it's something to do with the leather. Day after posting this, I was out again in the same jacket and again, I was warm, and it occurred to me that until I sold my Barbour recently, I found that it was not nearly as warm, and this with the belt, sleeves and neck done up tightly with a silk bandanna added.