Sweaty monster needs clothing

I've found the Rohan Expedition shirt, with "traditional" collar, long sleeves and button front, is excellent for hot days. Allows good ventilation, keeps the sun off and, being synthetic, dries very fast. Mountain Hardwear, Paramo and others do very similar ones and which is "best" will depend on personal preference. Rohan also do the Ultra T, which is astonishingly light and holds very little moisture.

Of the conventional base layers I find polypropylene the least clammy -- Helly Hansen Lifa is probably the best known. I'd agree that merino, nice as it is, just absorbs too much moisture in really sweaty conditions.

Sub-zero do a top that's even worked in Death Valley. I tried one and it was very good BUT abrasion resistance was crap. You got loose threads that were pulled from it if you wore something like a rucksack on top. I ven had a thread pull loose on the first day I wore it!

I accidentally went up a size so it was also quite baggy, which I'd recommend to help keep you cool.   

Is it better to wick sweat away in warm conditions or to allow evaporation to cool you? I've even heard cotton can be better in hotter conditions as the sweat evaporation cools. Not sure if a myth.

No, it's not a myth, but evaporation can have a cooling effect even if it isn't directly off your skin.  Liquid waterconducts heat away remarakably well though.

Where cotton is most typically a problem is it stays damp for a long time, but that's a bit of a non-issue in a heatwave.  You won't necessarily want to go to bed in the same top or put it on the next morning though.

There tends to be something of a cotton == bad perception in the outdoor gear world, starting with the rather hyperbolic "Cotton Kills!" beloved of doom-mongering merkins but spilling over in to places where it's actually okay.  And nice summer days where you will be sweating, the weather will stay fine and you want to keep as cool as possible it's okay. 

Pete.

"Not sure about the praticality of running in a trekking shirt mind "

Which was one reason I mentioned the Rohan Ultra T. Not actually styled as a running shirt, but would be excellent for that purpose imo and also good under the Expedition shirt on sunny but rather cooler days.

Btw the fact the shirt is a bit more windproof than a standard base layer and you can do up all the buttons, roll down sleeves etc. actually makes it comfortable over a surprising range of conditions.

Load of rubbish the only top to actually make me smell sweaty.

within a day i smelt sweaty which tbh really is not like me even after a few days in the same baselayer and with washing daily....

Yep like NiloC, I use the Rab Aeon Tshirts, come in long or short sleeve and they're mega.

Tried HH lifa, M.E Crux and a North Face version.....Personally didn't like them.

I know its perhaps not look the best on the hill, but I'm just putting it out there...but Nike Dri-Fit gear is excellent, and Adidas Clima-Cool isnt so bad either.....you'll look cracking in a gym, or on a street corner with some "scallies" aswell!

Bonus!

I've been living in Greece for 13 years now, as we tend to see tempretures up to the mid 40c's in the height of summer and the dog still needs walking i've had somne experience with trying to keep as cool as posible in hot weather while reasonably active.

Easiest way is to just throw on a cotton tee-shirt, the baggier the better.

If for some reason i've messed up my day and i'm out midday then i'll also throw on a long sleeved shirt over the tee-shirt.

Might sound a bit counter-intuitive layering up in summer, but if you look at the middle east you'll see most wearing lots of thin layers in the summer months.

Reasoning behind this is once the sweat has evaporated then you've lost it's cooling abilities, if you add another layer then your trapping the sweat to evaporate slower.

It does work in practice.

Don't forget a hat as well.

As a Brit i laughed the first summer as my Greek mates wore hats, my thinking being my heads hot enough already without adding a hat.

Now a wear a hat in summer

Agree with Guy H - the Expeditions are really good.  I have four, inc one short-sleeved version.  Excellent pockets, too - the best?  They are not the thinnest of shirts, but still very light, and I find really thin material can feel horribly clammy and cold if it gets wet and conditions have worsened - e.g. where one might have wanted a thin thermal vest.

Strongly suggest pale colours to keep cool, too.  Try touching different coloured cars on a hot day - dark ones are much hottter than white or silver.