Trying one - if it sucks or doesn’t work it is testament to marketing hype of hot weather base layers and it’s all your fault.
But seriously, have a 200miler coming up and expect it to be hot. Have wanted to try something so this is a reasonably priced option. I’ll even try it on the trainer with the Lasko fans first. Plan could be to wear this for the first nine hours or so then strip it off in the afternoon and have a drier jersey for the rest of the ride.
Just to be clear, I do not use them outside any longer. I use the modern hot weather jerseys. I only use these on the trainer now, with no jersey. Call me Right Said Fred.
I thought I said that above too, but a couple replies lead me to believe I did a lousy job of it! 
All good, I read that. Haven’t done the mesh jersey thing yet, but probably should. Need to wear my team jersey, which has a mesh upper and underarms (which definitely helps). Figure I can try one of these. Have had my eye on the Rapha versions but they’re almost twice as much, so this is a reasonable “try” and could be great for the trainer.
I’ve heard that the whole base layer “cooling you down by creating a layer between you and the jersey” is marketing babaloo.
The best way to cool down is to expose skin, especially sweaty skin.
So want to keep cool during those efforts? Open up the jersey and expose that chest baby.
Well, it’s to expose sweaty skin to airflow. Or to cover skin with cool water and expose to airflow. Without the airflow, it doesn’t matter what you do.
Of course, I think that would go without saying since we are talking about cycling and not standing still 
Ever ridden uphill in 95-degree heat, afternoon sun, and with a tailwind? I suffered heat exhaustion last summer in that exact condition. While I was moving along just fine, zero airflow because the tailwind effectively made relative airflow nil.
Also… the trainer.
I have, but usually not too bothered by heat in that sense. But of course has to use some common sense if its that warm, both in preparation and what weather you are used to etc.
You don’t use a fan on the trainer…?
I do. My point was that airflow is required for evaporative cooling. Simply cycling on your trainer with your shirt off isn’t going to keep you cool. We aren’t disagreeing on anything, just amplifying your statement about exposed skin. Exposed Skin + Airflow. Don’t take the airflow for granted…
Only reason I’m harping on this is I had an athlete whose FTP on the trainer was 30W lower than outside, more than 15%. He couldn’t get through even 4x4 threshold intervals, even at the lower FTP. Turned out he didn’t have a fan at all. He “likes it hot” and “doesn’t mind the heat”, but didn’t understand that he was getting no cooling, and there’s actually a “bubble” of increased humidity that traps heat when you don’t have any airflow on the trainer (or on a treadmill). The giveaway was that he told me there was a massive pool of sweat under the bike when he finished the workout. If you’ve got enough airflow on the trainer, the sweat dripping off you should be minimal.
Cheers!
Makes total sense, then we are on the same page! 
This is a message we need to find a way to spread. So many riders think “pools of sweat” is a badge of honor. It’s like the “look at my disintegrating handlebars” posts.
I have no affiliation with this company I just think these baselayers are worth their weight in gold. The 3d-ness of the mesh holds the jersey off the skin so there is no clammy feeling of the jersey sticking to you and when I compare them to other baselayers I feel like I get better airflow against the skin (through the jersey and the opening in the mesh.). Check out the second pic, you can see the open-ness. Most ‘mesh’ baselayers I’ve tried don’t have big openings like these to let the air through to your skin.
110%, the “Pool-O-Sweat = Winning” idea needs to die a harsh death. Outside of deliberate heat training, this is a problem to be corrected, not something to brag about.
I know not everyone needs the wacky setup I run, but I suspect many riders could benefit from an improved fan setup. Proper blower fans instead of poor circular for one, proper placement for another (including the back which is a HUGE surface area prime for cooling) are the most common ones I see as easy gets.
Yesterday afternoon it was 100F / 38C, a little warmer on the tarmac, and here are two EARLY MORNING riders that decided to “embrace the heat”
and
She does a handful of afternoon rides a year 
Both with post ride pics of them dripping sweat in their garages 
not sure I want to comment on her Strava that it only sucks at 95+ or 100+
Yep. As you saw in the pain cave thread, I run three proper blowers now. I have no issue completing hard interval sessions in my garage when it’s in the 80s with humidity. The air flow, particularly on the back, makes all the difference.
Also the difference between 81 in the shaded garage and 81 outside in bright afternoon sun can’t be understated.
No affiliation here either, but I was gifted a Hyperthreads kit and it is very comfortable. I actually prefer that kit to my high-end Assos kit.
I’ve done that with two fans, but adding a small 3rd fan for the back of head was nice. I do need some heat acclimation, and start seeing really strong power numbers after 6-8 weeks of consistently riding in 85-95F / 29-35C temps. I prefer wearing a full summer kit in the garage on the indoor trainer. Don’t notice much difference riding outside in mid day sun in mid 80s, versus the garage. Peraps because of the extra cooling outside? I don’t know.
That said it is a dry heat. Compared to Texas or the Midwest, there is not a lot of humidity down in San Diego where you are, or up here in Sacramento.
and FWIW… my best ramp test (while I was doing them) was completed in September when the garage was 80-82F / 27-28C. After doing SSB1 mostly in the garage, with some easy outside 100F / 38C rides on the weekend.
Normally true. Been 70% or so the last week. Can get that way here in August/September, and it sucks. Not like Alabama sucks, but it’s all relative.
yeah as you know its usually 60-80% humidity in the mornings but temps only 55-65F / 13-18C. And afternoons 10-30% unless you are right on the coast in/near fog.
Sunday it felt humid but I didn’t check %, and we did get a few drops of rain. Figure a monsoon came in off the Gulf of California.
Two days ago it was 40% humidity and 88F when I went out for 2 hours and did 3 sets of easy-ish 20/40s. My kit was soaked when I got home.
