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Old 06-25-06, 09:27 PM   #1
bccycleguy
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Does the colour of a cycling cap/bandana matter?

Summer has finally arrived in the Great White North and we are looking at 32+ degree C (90+ degree F) temperatures for the foreseeable future. I cooked my brain today on midday 55 km (35 mile) ride.

When it's hot I usually wear a sweat band, and I often wear a cap or bandanna under my helmet because I hate it when sweat trickles across my scalp (I'm bald on top). My Halo cap (cool max) is black and it's hard to tell if I'm hotter with it on or off, like wise with a cotton bandanna. I wonder if colour has any influence on how hot it feels. The sun shines through the helmet vents so the black cap is heating up but black might be a better colour for radiating heat. What about white, maybe it would would better as a helmet liner, but it might hold the heat too. Maybe the colour is irrelevant because it's mostly covered by the helmet.

I would think people who ride in hot temperatures most of the time have figured this out. What do you think.
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Old 06-25-06, 09:38 PM   #2
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Technically, yes. Black would be the hottest color.
However, on such as small contact area, i wouldn't care
Your black cycling shorts are heating you up more.
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Old 06-25-06, 09:40 PM   #3
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I lived and cycled in Winnipeg for many years where many of the summers had days in the high 30s.

I purchased a black sleeveless jersey which I thought would be a good choice for summer riding ... because it was sleeveless! At the same time I wore a black helmet.

After one particularly hot summer, I rushed out and purchased a pale lavender sleeveless jersey and a yellow helmet. I've never gone back to a black helmet again, and I never wear the black jersey when the temps go over about 25.

If I were you, I think I'd look for something white, or at least light.


BTW - Black holds the heat .... white reflects it.
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Old 06-25-06, 09:47 PM   #4
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I found a hot pink bandana on the side of the road two years ago. I washed it and used it for the rest of my trip. It was much better than my blue or green ones. I have no evidence, but bright yellow or pink seems to keep bugs away better. They seem to love my green one. Your cap should be light on the outside, but the underside of the bill should be dark to prevent glare.
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Old 06-25-06, 10:10 PM   #5
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Actually, nm+ has it wrong. Your head is an incredible radiator, and you can get as much as 65% of your heat loss from your scalp. It might be a small "contact area" but there's a tremendous amount of blood flow through it. But a black bandana or cap under the helmet won't make much difference. I'm thinking that the type of fabric you are wearing will make a bigger difference than black (which nm+ tries to tell us will make us really hot because it'll absorb all that sunshine on the top of your skull.)

But I think what is really making you feel hot is riding along on a hot day thinking about how the sun is shining in through the helmet vent holes making your head hot. I'm pretty sure that the vent holes are there to allow more air to flow through the helmet, possibly cooling your head?

So you have a sweaty bald head with lots of capillary circulation through it. That's called radiation.
You have vent holes in your helmet allowing air to pass over your head. That's called convection.
All that's left is conduction, which would be stuffing your head in a bucket of ice water.

You just have to face it: if the weather is hot, you're gonna be hot, too. Either suck it up and sweat like a pig, or stay home and watch sports on TV.

(nm+ is from the San Juan Islands in the Pac NW. It doesn't get real hot there, and when it does the natives shrink away, complaining, its too hohhhht! I can't bweeeeethe! And that's at 75 degrees.)
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Old 06-26-06, 12:28 AM   #6
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It's more that the colour, a black cotton bandana has low thermal mass, a black car surface can get hot enough to fry an egg.
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Old 06-26-06, 08:45 AM   #7
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One of my neighbors has a blcak car. Its supposed to be 92 degrees today. I'm gonna give the fried egg thing a try. After the fight, I'll have the priviledge of coming back here and telling Peter Pan he's/she's full of fried eggs.
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Old 06-26-06, 09:53 AM   #8
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I don't think the color matters as much as the material the cap is made out of. I use the coolmax Headsweats. They do an excellent job wicking away sweat and cooling your head. I wear either black or dark red headsweats and do not feel overheated, even on the hottest of days.

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Old 06-26-06, 10:02 AM   #9
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Maybe an aluminum foil cover over the bandana to reflect the sunrays coming in through the vent holes?
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Old 06-26-06, 10:05 AM   #10
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Just a thought: the other day I was in a LBS and I had left my bike, helmet, and bandana in the front of the store. I heard someone call out "hey, who left their gang colors up here?" It never occured to me I was wearing gang colors as I ride through town. YMMV.
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Old 06-26-06, 02:35 PM   #11
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My guess is that the fact that your skin is protected from the sun has a bigger effect than the colour of the fabric that is doing the covering. A black bandana probably does absorb heat from the sun, but I would rather the material absorb that heat than my skin.

I would not be surprised to find that the material makes a difference For hot-weather biking, I find a synthetic jersey cooler than a cotton T-shirt, probably because synthetic materials don't absorb sweat.
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Old 06-26-06, 10:18 PM   #12
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I'm stoopid, I guess. I just don't see how the black bandana, under the helmut, is absorbing heat. Black objects "absorbing" heat are doing so from the sun, not from heat. Light from the sun is the energy, energy is turned into heat through any number of differing processes. Color is not a process, but is visualized when reflecting light (black actually is the abscence--or non-reflectance--of light.)

Maybe you guys can send your ideas to the people that make household insulation. You know that fluffy pink stuff inside your walls. Maybe if they start making it black it will absob more heat and be a more effective thermal mass.
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Old 06-27-06, 07:29 PM   #13
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Quote:
Originally Posted by chromedome
Color is not a process, but is visualized when reflecting light (black actually is the abscence--or non-reflectance--of light.)
You hit the nail on the head. Black does not reflect the light, it absorbs it. Light is energy. Hence black absorbs more of the sun's energy than other colors. And what happens when you dump energy into something? It gets warmer! So the color does matter.

Black also radiates energy better than other colors, but to take advantage of this property the black object has to be hotter than its surroundings (and when the sun is in the sky the sun is part of your surroundings from a radiative point of view). This is a good strategy for, say, the cooling fins on a motorcycle engine, but not so good for your head.
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Old 06-27-06, 08:18 PM   #14
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So today I tried it out.

I took the mercury thermometer off the back of the house, cooled it off with water to 70F, wrapped it in a (room temperature) black Tshirt, stuck it in my green helmut, and put it in the sun for 30 minutes. It measured to 86F.
Then I cooled it off again to 70F, wrapped it in a white Tshirt, stuffed it in my green helmut, and put it in the sun again for another 30 minutes. Guess what? 86F.

So I started over. Did the same thing, but left it in the sun for one hour each time. Guess what? 86F.

The ambient air temp today was 84 degrees according to the TV. The other thermometer (one of those cheapie springy things that have wax in them) we have I put in the sun next to the helmut. Stayed at 110 the whole time.

Now, of course, it wasn't terribly scientifically controlled, nor did it gather much in the way of data to satisfy a statistician's idea of a data set, but I'm satisfied. Still.
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Old 06-27-06, 08:24 PM   #15
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Quote:
Originally Posted by chromedome
Maybe an aluminum foil cover over the bandana to reflect the sunrays coming in through the vent holes?
Yes and it will keep the CIA satellites that George Bush just had launched from reading your mind.
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Old 06-27-06, 09:01 PM   #16
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Solar absorption & radiation

Quote:
Originally Posted by chromedome
So today I tried it out.

I took the mercury thermometer off the back of the house, cooled it off with water to 70F, wrapped it in a (room temperature) black Tshirt, stuck it in my green helmut, and put it in the sun for 30 minutes. It measured to 86F.
Then I cooled it off again to 70F, wrapped it in a white Tshirt, stuffed it in my green helmut, and put it in the sun again for another 30 minutes. Guess what? 86F.

So I started over. Did the same thing, but left it in the sun for one hour each time. Guess what? 86F.

The ambient air temp today was 84 degrees according to the TV. The other thermometer (one of those cheapie springy things that have wax in them) we have I put in the sun next to the helmut. Stayed at 110 the whole time.

Now, of course, it wasn't terribly scientifically controlled, nor did it gather much in the way of data to satisfy a statistician's idea of a data set, but I'm satisfied. Still.
quoted from here:

Heat Absorption vs. Color

Question: Why does the color Black absorb heat and White reflect heat? What
are the physical properties behind this fact? I have seen some Arabs where
Black robes in the desert -- this seems to defeat the purpose. Do they wear
them because black protects more against harmful UV rays?
---------------------------------------
First of all I have no idea why some Arabs wear black robes in the desert. It seems counter-productive...but oh well, different strokes for different folks. Anyway, the color that we observe (i.e. the color of a particular object) is really only the light that is reflected from that object. For example, a red ball appears red because when white light strikes it, all of the light is absorbed except for the red frequencies/wavelengths which are reflected into our eyes. A white light is made up of all visible (and invisible) wavelengths all mixed together. So an object that appears white, is reflecting all of the incident wavelengths and absorbing nothing (or very little). A black object, on the other hand is absorbing all of the incident wavelengths (along with all of their energies) which causes it to heat up. That is why snow does not melt in cold weather even when the sun is falling directly on it. All of the incident light energy is reflected away and none (or very little) is absorbed.


I hope that helps.
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Old 06-27-06, 09:27 PM   #17
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Quote:
Originally Posted by chromedome
Maybe an aluminum foil cover over the bandana to reflect the sunrays coming in through the vent holes?
No, that is to foil (pun intended) mind control rays.
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Old 06-27-06, 09:33 PM   #18
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Oy.....arrrrgggh......errrrffff......

The way that I understand the original post is that the bandana is on the inside of the helmet, thus not having much sunlight on it (except through the vent holes.)
Did the thread change from that?

If the concern is the color of the cap/bandana without the helmut, or the color of the helmut, thats a different story. To my mind, its the color of the material that is coming in contact with sunlight. I think what Sailing home said about color spectrum and light should explain that.

But conversely, do you wear a black helmut, cap, bandana in the winter (on cold sunny days) to warm your head? Why isnt all winter clothing solid black? Why is asphault cooler under the shade of trees than that which is out in the sun? Does somebody with all black hair have a cooler head if they wear a hat than one who doesn't?
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Old 06-27-06, 09:37 PM   #19
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[QUOTE=sailinghome]q That is why snow does not melt in cold weather even when the sun is falling directly on it. All of the incident light energy is reflected away and none (or very little) is absorbed.


But snow does evaproate in even extremely cold weather and the evapoartive process is excellerated by convection.
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Old 06-27-06, 09:39 PM   #20
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how about getting one of those umbrella holders that mount on your handlebars?
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Old 06-27-06, 09:56 PM   #21
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Quote:
Originally Posted by chromedome
So today I tried it out.

I took the mercury thermometer off the back of the house, cooled it off with water to 70F, wrapped it in a (room temperature) black Tshirt, stuck it in my green helmut, and put it in the sun for 30 minutes. It measured to 86F.
Then I cooled it off again to 70F, wrapped it in a white Tshirt, stuffed it in my green helmut, and put it in the sun again for another 30 minutes. Guess what? 86F.

So I started over. Did the same thing, but left it in the sun for one hour each time. Guess what? 86F.

The ambient air temp today was 84 degrees according to the TV. The other thermometer (one of those cheapie springy things that have wax in them) we have I put in the sun next to the helmut. Stayed at 110 the whole time.

Now, of course, it wasn't terribly scientifically controlled, nor did it gather much in the way of data to satisfy a statistician's idea of a data set, but I'm satisfied. Still.
You did a good experiement, but not the right one. Try this: get two aluminum soda cans, drink soda. Paint one white and one black. Fill with water and freeze. Put in sun and see if they both melt at the same time.

In your experiment, both times the shirt + thermometer system was allowed to come into equilibrium with the ambient radiation field, which was the same in both cases, so the temperatures were the same.

Just to be clear, I don't think the color of the cap makes a big difference since it is mostly covered by the helmet. I'm just talking physics.
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Old 06-27-06, 10:13 PM   #22
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Watch the movie Cruising (1980) starring Al Pachino. The scene where the shop-keeper tells Pachino what the colored bandanas mean should explain it all.
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Old 06-27-06, 10:15 PM   #23
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I just tried to recreate a similar environment to wearing a certain color of head covering under a helmut.
A person's head will be in a radiation field no matter where its at, which would've been in the mid 80's in my little experiment. In reality, a head would've been somewhere between 98F and 103F, depending on hydration, work, and so many other variables, because of my own body temp.
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Old 06-27-06, 10:23 PM   #24
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The color of the bandana and which rear pocket it is in can matter a lot in places like Fire Island, Key west, and West Hollywood. I prefer a terrycloth sweatband. I have enough hair to prevent funny tan patterns on my scalp.
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Old 06-28-06, 07:29 AM   #25
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Quote:
Originally Posted by chromedome
I just tried to recreate a similar environment to wearing a certain color of head covering under a helmut.
A person's head will be in a radiation field no matter where its at, which would've been in the mid 80's in my little experiment. In reality, a head would've been somewhere between 98F and 103F, depending on hydration, work, and so many other variables, because of my own body temp.
The thing is that in a case like a person whose body has a built-in cooling system with a hat on their head (instead of a little thermometer), you don't reach thermal equilibrium with your surroundings, so your experiement wasn't answering the question you should have been asking.

Also keep in mind that mid-80s is pretty darn cool for an object sitting in direct sun. Was it snowing at the time?
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