What cools our bodies?
Convection, Conduction, Evaporation and Breathing.
When it is cold outside these are our friends, but how can we use them to help cool ourselves down in a hot climate or while we are outdoors during a heatwave?
First, lets understand how these cool our bodies.
1) Convection - This is heat loss by the wind hitting the skin on our bodies. Also by air moving around inside our clothing.
2) Conduction - We can lose heat by transferring our energy to a cold surface, perhaps when sitting on the cold ground, leaning against a cold wall or holding cold items, such as walking poles or ice axes. Even our layers when wet will help us loss heat by conduction.
3) Evaporation - We loss heat from evaporation of sweat or water off our skin. Sweat and water can cool you 24 times quicker than air. Evaporation can be our Friend and Foe, when it hot it is our friend!
4) Breath - We can lose heat from our breath, so just breathing helps us cool down.
I have recently observed Blackbirds in my garden during a heatwave. This mature Blackbird had his beak wide open, I was told that the Blackbird does this to help him cool down. So there you go, during the next heatwave perhaps walk around with your mouth wide open! Join me in the next article that discusses ‘How to prevent flies from going into your mouth during a heatwave’.
So how can we use this information to help us cool down?
1) Convection - If there is a breeze or a wind, expose as much skin as legally possible. The air blowing against you skin will remove warmth from your body. Wearing shorts and t-shirts (keep in mind sun protection), pulling up long sleeves and venting by opening up zips.
Another way is to wear baggy clothes. With baggy clothes you find (A) The larger mass of air in the clothing will not get as warm, as if you had tighter fitting clothes. (B) Being baggy, air in the clothing will move around. You will find the warm air will exit the clothing and cooler air will enter, helping to regulate your temperature.
2) Conduction - If you are stationary you maybe able to find a cooler surface to lay, sit or lean on. If you are moving, it is a little more difficult. Although it is includes evaporation you can use damp clothing. start small like a damp scarf, damp socks (at night), damp hat or if you are really hot a damp/wet shirt.
3) Evaporation - Basically sweat or water on our skin will cool you when evaporation occurs. During evaporation liquid turns into water vapour. When moisture on our skin evaporates, the change that takes place creates a cooling effect on our skin. So assisting evaporation by keeping our skin damp will help. Selecting base layers that will not wick your sweat away is oneway, instead select base layers that aid in keeping your skin damp by pushing sweat back towards your skin. The other option is to use water and dampen or ‘wet out’ your clothes, depending on how hot it is.
4) Breath - Simply walk around with your mouth wide open and prey you don’t get too many flies going in. Seriously though, breathing through your mouth rather than your nose may help you cool down. To be honest this is something I need to be more aware of and try in the next heatwave. I do know that when riding the bike the odd fly does get in!
Clothing to help.
1) Convection - Linen clothing and cotton polo shirts are good ways to get air to the skin because of the fine holes in the material. However, these aren’t considered to be performance outdoor clothing but when you are dealing with much warmer temperatures then they can be good choices. The problem though is that they are not very good or even dangerous if the temperature drops, so they need to be used when the temperature is consistently high.
The other down side is that they could be a problem with sun protection or lack of it. Due to the open structure of the material, sun protection will be an issue. Also, bugs can get through the open material as well.
Another way to get protection from bugs, the sun and also cool down is by using clothing made with a weave rather than a knit. Clothing made with a poly-cotton material such as a shirt, or a windproof made with a weaved nylon can be effective when worn next to the skin. The stiffer material allows air to move around more freely than knitted material, keeping you cooler. Tighter knitted material will trap air and keep air still so it can warm up and in most cases wick the moisture away preventing evaporation, so it won’t help in cooling you.
2) Conduction - Perhaps by wearing lighter weight clothing that are thinner or by removing certain clothing, you may benefit from convection. This way you will make better contact with cooler air and surfaces.
3) Evaporation - The function of outdoor clothing has to be completely flipped upside down when going from cooler conditions to warmer conditions. Instead of removing moisture in cooler conditions it needs to push the moisture back to the skin in warmer conditions. It is down to the individual user to decide when it is the right time or really the right conditions to flip his or her clothing’s function. Having a flexible clothing system that can flip between the two functions of preventing or helping evaporation can be very helpful.
On a days walking adventure you may start in a valley with high temperatures such as in the high 20’s or 30’s C. However, when you reach the summit of the days mountain it might be 10 C and then when you are back down in the valley you are back into the high 20’s or 30’s C again.
The common wicking base layer that wicks moisture away from your body which is vital in cooler conditions will prevent evaporation occurring in warmer conditions.
Some base layers can be worn in such away that they draw moisture back to the skin. This way evaporation can occur and cool you down, these base layers will probably be a technical knitted polyester.
More on base layers later!
To cool yourself down using evaporation one option is to use clothing made with materials that hold onto moisture. One common and easy to get hold of material that holds on to moisture is cotton. By using cotton there is more chance of keeping your clothing damp in warm conditions and hence keeping you cool. Polyester will not hold on to moisture for very long and will dry out quickly. With this in mind, when you plan to ‘wet out’ an item of clothing to help cool yourself down, cotton will stay wet for longer than polyester or nylon.
4) Breathing - Breath through your mouth rather than your nose and don’t cover your mouth with tubes or buffs.