Heat is always being transferred from warmer to cooler. That’s just the way it is. We can transfer heat to the environment OR we can absorb heat from the environment. But either way, there will be a transfer.

Heat production and heat loss

We have two different types of body temperature. Body core and skin temperature. Our body generates heat and strives to maintain a core temperature of approximately 98.6f. Though this is not a precise figure, we can only deviate from it very slightly. Even 2 degrees over or under 98.6 makes a huge difference in our well being. Our skin temperature will generally range from 91 to 93F or so.

Our body is always generating heat. It uses what it needs to maintain our normal core temperature and shunts the rest of the heat to atmosphere. This means that we are constantly giving off heat in various ways.

Our skin radiates heat. We also lose heat with each breath we exhale (breath is hot, not cold, no matter what the gum companies want you to believe!)

In normal outside temperatures of up to approx 68-70F, this is enough for us to maintain normal body temperature.

If our body temperature rises too quickly (ie exertion or exercise) or if the heat index is too high, this method of heat loss is often not enough. Our sweat glands kick in and our main method of body cooling then depends on evaporation of sweat.

As the sweat evaporates, it takes heat away with it. This cools the skin which in turn cools the blood circulating near the surface. The cooled blood returns to the core and muscles, cooling them. And the deed is done.

The mesh paradox

In very hot and dry temperatures, say over 100F, your body absorbs the heat from the air (convection) as well as from the sun (radiation). The higher the airflow ie the higher your speed, the greater this effect. Remember that heat is always flowing from warmer to cooler. If your body is warmer than the surrounding air, it gives off heat. If it is cooler, it absorbs heat.

The dilated blood vessels that were meant to carry heat to your skin now absorb heat from the hot air and carry it back to your core. Though there is evaporative cooling going on, you are absorbing more heat by convection than you are losing by evaporation. In fact, sweat probably evaporates too quickly and becomes insensitive sweat.

So it’s like a simple equation:

Convection heating adds a certain number of heat units.

Evaporative cooling removes a certain number of heat units.

As long as you are removing more heat units than you are adding, you’re ahead of the game. But at highway speed with a temperature of 110F of dry heat, you are absorbing more heat units by convection than your are losing by evaporative cooling. Not good.

On the other hand, it may feel comfortable commuting at low speeds in the city wearing mesh because convection heating resulting from airspeed is lower and evaporative cooling has more effect. But this is only true at relatively low speeds.

At highway speeds in high heat, your body ramps up the sweat mechanism, but it cannot supply what is required. Your system come under stress. You become at risk for heat exhaustion or heat stroke.

The hot ticket is to shield yourself from the convective heat-gain while benefiting from the evaporative cooling. When deciding how much to open your vents for some evaporative cooling, remember that your goal is limit airflow over your body to just what is needed. A little airflow goes a long way.

The dreaded ground effect

It’s also imperative to insulate yourself from the heat due to ground effects and any heat given off by your motorcycle.

The ground absorbs heat and radiates it back. As you ride over a road in a temperature of 110F, the heat radiated from the road surface at the height of twenty five to thirty inches can be over 140F or more. That literally means that you are riding over an invisible layer of 140F heat! This explains why your feet may feel very hot. If you are wearing ventilated pants ie mesh, you will be absorbing heat by convection from the passing air as well as by heat radiation from the ground.

This temperature will heat the material on your regular riding pants as well. At these temperatures, a layer of Cordura may not be enough to insulate you. You may find yourself with heat blisters on your legs. Wearing a layer of long undergarments under your riding pants or even jeans will help insulate your from this type of burn.