Does A Base Layer Keep A Rider Cooler in Hot Weather
 

I have always felt that a base layer holds your sweat closer to your body which helps regulate cooling. You do see a lot of riders who do not use a base layer when it’s hot. I wonder if it doesn’t make a difference.

Only if there's wind or airflow

It was either a podcast with the lead technologist from Pearl Izumi or a VeloNews tech podcast where the point was made that most cooling comes from sweat evaporation due to the large energy required to evaporate water. Therefore, having water evaporate as close to the skin as possible rather than clothing is best. A base layer transports water from the body to the outer jersey layer and so reduces cooling. That’s good in cold weather, bad in hot.

I'd think a base layer will just keep more sweat in which in turns means that you are holding more heat next to your body. For anything over 70ºF I'm only wearing one layer.

Even if the sweat isn't evaporating at a fast rate, just the fact it can drip off of you means it's carrying heat away from you.

I have always found that a base layer is hotter.
You can still ride with one in quite warm temps, but it is definitely cooler when removed.

Opinions are split something like 50/50 among the people I've talked to about this. Including a lot of hikers and climbers.

I have a few base layers with high tech yarns that spread moisture out over a large area to evaporate more quickly. Now I haven't done anything scientific like measure my skin temperature with and without, so all I can really say is it's comfortable even on hot days.

Also a lot of base layers are UPF 25 to 50, so you don't have to use chemical sunblock (or reapply on a long day). I don't like the way it feels on my skin.

there's always an 18+mph airflow when I ride(unless I have a tailwind).

Never worked for me, I was much hotter when I wore the base layer. Not aero but I cool off by unzipping my jersey most of the way, let the air flow. Very humid here, not much evaporation, that probably makes a difference.

Base layers make sense for hiking and slower outdoor activities where you might want a more rugged outer clothing to deal with environmental factors. I used to always be particular about my base layer when I used to do a lot of hiking, rock climbing and other such in the woods. Not so much anymore as those activities have gone by the wayside.

You certainly don't want sweat piling up next to your body, But the looser outer clothing you wear to avoid abrasions from limbs, thorns and other such you might rub against won't rid you of the sweat if it's not touching your body. So that is where a base layer comes in.

In cycling on a road bike usually the clothing is form fitting and snug. There is no need for a base layer. Unless, you like to wear loose clothing when you ride your road bike. IMO of course!

All a base layer would do in the southeast is hold more water. I can wring out my gloves and socks after an hour. Another layer to hold even more sweat is completely pointless. And nasty.

I almost always wear a base layer. I tend to "run cool" and rarely feel like I'm hot or overheating on the bike. I mostly like the additional compression and feel of a base layer, plus it keeps jersey seams and bib straps from chafing on my skin.
When I ride without one now in hot weather, the jersey feels like it's sticking to my skin more.

I do all my riding in the early morning, so I rarely ride in temps much above 80F. I suppose if I were riding in mid-day summer sun with temps in the 80F+ range, I'd likely ditch it.

This. I always wear one, but it doesn't get particularly hot in the PNW.

OP try it, if it doesn't work for you, don't wear it.

Same here. Todays ride will be 62-98 deg. I will start with base and then remove ~ 85deg.

Same deal here. I always ride with a baselayer and sunsleeves.

My rides are typically in the evenings on weekdays and early morning on weekends, so I ride anywhere from 60 - 90 degrees in SoCal. I too like the feeling of the compression and the extra layer between the jersey. However I'm the type of guy that always wears an undershirt.

I don't feel overheated or overly sticky. One thing I do like is the wind hitting the baselayer and the mild cooling sensation, but it's entirely subjective.

It might be a regional thing. I live in the PNW. I would consider an 80 plus degree day very hot. Many places in the country 80 degrees is on the cooler side of summer temps.

I'm not taking a position on base layer or no, but you've got the physics wrong. The cooling effect comes from the heat of evaporation - the energy required to transform liquid water to vapor - resulting in a net decrease in heat (well, really, enthalpy) on your skin. Just dripping off has no effect on your skin temperature.

Which is what you want for maximum cooling.

You are only looking at one aspect of physics, cooling from evaporation. There is another aspect of physics too, moving the heat away from you.

So letting the sweat which contains a lot of heat drip off of you will keep you from getting hotter instead of retaining all that heat around you. I suppose if you are going to get me on a technicality, then that isn't cooling per se, but simply a way to get less hotter..

No, sorry, that's not right. The sweat and your body are at the same temperature, so moving it away does not cool you. The sweat, sitting on your skin, is not transferring heat to your body, so removing it has no effect. If we adjust for the fact that your skin temperature is a little lower than your internal temmperature, we'd have to adjust for the fact that the sweat temperature is also lower than your internal temperature for the same reason

The heat of evaporation, on a mass normalized basis is enormous.

Trust me on this one, it's my profession.

Sweat cools to below skin temp the moment it's secreted because evaporation, and remains much more efficient at conducting heat from the skin than air or your jersey.

When it's hot here, it's usually because we have wind blowing in from east of the Cascades where it's pretty arid. So our hot days are dry ones where our sweat does the job it evolved for, cooling by evaporation.

Yep, and keeping a wet cloth on your skin, helps keep you cooler.

I live and ride in the hot part of Asia. No, base layers dont help keep you cool.

Which is why I have occasionally,on hot (>90) days dumped water down my back and on my head on sun-drenched climbs, to augment my already copious perspiration. I was amazed how well it worked the first time I did it. You just have to remember which bottle is water and which is sports drink!

Yes it does:bang: