Casual and Cool: Polyester or Cotton/Merino?

No textile expert but there's no free lunch and the weave makes a huge difference. Like windshirts, try the Darth Vadar test and see how much resistance the fabric gives when breathing through it.

In the front country, I prefer cotton and cotton/nylon blends when it's hot. When traveling, including through India both in winter and in its oppressive summer heat, Eddie Bauer 100% cotton button down dress shirts are my personal preference.

I can wash them in the sink and typically they are either dry, or dry enough to wear by the next morning. If it's cool and humid, it may take a bit longer.

My pantalones preference du jour for front country travel are a nylon/cotton blend pant from Kuhl called "Revolvr"

T shirt I wear is Duluth Trading company's "BUCK NAKED PERFORMANCE CREW UNDERSHIRT" (copy/paste not yelling) nylon/lycra blend. Black or white perform about the same in regards to heat and neither smell.

Wright coolmax socks.

Yeah the weave/knit matters hugely. I second breathing through the material and seeing how much air makes it through. It's crazy how many hot weather shirts you try to breathe through and it's like breathing through a plastic bag. Yeah it's lightweight material but no air gets through!

Cut matters too. Loose cuts will allow airflow whereas slim cuts won't.

As far as fabric material I don't know if it will matter that much between poly and merino.

Polo style "golfing" shirts made of a loose polyester mesh weave are great for SE US summers (hot and HUMID) As well as those made of poly and cotton blends. Also, look for those made of Pima Cotton. Very soft and breathable.

Or, How about the "fishing/hiking/safari" style shirts? Like those from RailRiders, ExOfficio, Patagonia? I have the Patagonia Sol Patrol II shirt. It's a polyester weave rather than nylon and very breathable. i find the nylon ones to be pretty stifling. Columbia also make polyester shirts of this style. Short and long sleeve style button ups in poly or poly/cotton are great.

Patagonia has a ton of nice "front country" style shirts on deep discount right now. Look under their Web Specials page. (I really like Patagonia clothing. Fits me well. And I like how they size up their layers so you don't have too. If you wear a small down jacket, you can order a small hard shell and it will be big enough to fit over the down without sizing up to a medium.)

I have a Columbia polyester button-up shirt. It smells. I wear it 10 minutes and it stinks to high heaven. This doesn't happen with my nylon shirts. They take a while longer to smell bad and never smell quite as bad. My merino wool t-shirts take even longer to stink and the fumes seem not to waft around me in as large a sphere of influence.

Disregarding the smell.. as I can wash them daily and it's better.

I just wondered about this topic in general, if maybe for things like travelling in very hot weather, moderate activity where you are still sweating etc are better with a mixture of cotton/merino and polyester or polyester only.

But the biggest problem for me is the weave, if I compare my old Marmot Windridge shirt to my Rab Aeon Tee (very dense), they are woven completely different but it's hard to tell which is more suitable.

That all those manufacturers have their custom labels and funky names for garments does not really help.

For direct sun, you want a tight weave with thin fabric, you don't want to see a ton of light shining through.

If you aren't going to be in direct sun all the time, you want a very open weave shirt.

Either way, it's cotton all the way for me. Nothing breathes as well as cotton if you are talking tightly woven shirts. Cotton/polyester blends are also very good.

Look at the patagonia AC shirt.

Check out some of the polo style shirts from athletic brands that are marketed to golfers like UnderArmour, Nike Dri-Fit and Champion C9. They're typically all poly, and will fare much better than anything cotton, merino, or blending the two.
Some of the cotton/poly blends may feel and look better unless you get sweaty and they stick to you, since they will absorb moisture the straight poly doesn't.

Yes, lighter colored, thinner, more breathable, and loose helps no matter what the fabric is.

I prefer blends between synthetic and natural the most, thought straight nylon KNIT fabrics that wick are pretty good too. For the natural fiber, i prefer it to be linen because it doesn't stick as much as cotton, feels drier more quickly, is stronger, and a bit better odor prevention. Tencel is a decent alternative to linen.

But even (all) linen isn't ideal in very humid and hot weather, some synthetic helps. I have a 65% polyester and 35% linen very breathable, thin dress shirt–works great in humid, hot weather. It would be even better if the synthetic was nylon and also wicking (the polyester they used in this shirt isn't the wicking kind, but the shirt still wicks because of the linen).

If stink is not a factor for you, OR Echo shirts are pretty good. They have polygiene treatment, which is pretty durable for anti odor treatment, but will eventually wear off if you keep clothes for a long time. I don't think there is a truly permanent anti odor treatment for synthetics. However, both Merino and linen excel in that area.

Copy and paste from an older thread on the subject:
"The best that i've found are these in order: Synthetic-linen or synthetic-hemp blends, nylon-tencel blend, and Under Armour KNIT nylon "Iso-chill" shirts (very breathable, very wicking, pretty quick drying, and actually feels cool).

Unfortunately, the first two options tend to be pretty hard to find, and the last is fairly expensive (i bought my shirt on clearance)."

I should add that dri release stuff is decent (the ones with a little cotton), but i wish they wicked a bit better. Really good wicking fabric will immediately absorb and really spread out moisture put on the surface. My dri release stuff doesn't absorb as fast, or spread the moisture as much, as some of my good all synthetic wicking stuff or synthetic/natural blends that have a higher percentage of natural fiber.

They are coming out with more and more supposedly "actively cooling" fabrics, but i haven't tried too many because they tend to be rather expensive, and i live in a high humidity area, which reduces effectiveness of a lot of those type of shirts. The Under Amour Iso chill knit nylon shirt is supposed to be in that kind of category. I do like it a lot.

Christopher:

First all, regardless of labeling (e.g. "Coolmax") — nothing will keep you comfy and cool in truly hot/muggy weather. This is probably obvious since we will just sweat no matter what we wear — or even if we go topless!

The big difference in performance is how quickly a given material will dry enough to make you feel OK again when you hit the shade or get into an AC room. Cotton saturated with sweat will cling uncomfortably to your skin far longer time then poly or wool. Wool performs better but it can also warm you up more in warm climates. My choice for both hiking and casual wear is 60/40 poly/cotton blend. I get the quicker-drying performance of poly and the comfy feel of cotton.

Over the years, I've traveled all over the world with my poly/cotton tees. They dry quickly when washed overnight — so I only ever bring two (one on me and one in the pack) for even the longest journeys (7 months). I highly recommend this blend for casual wear: hiking, traveling or in town.

Thanks for your suggestions. Is cotton generally cooler than merino?

The rab meco 120 is light but it says "warmth of merino"

And yes, the Rab Meco seems to be warmer than a normal cotton tshirt.. could be that it is better after some washing, as my cotton tshirts are rather washed out and I suppose they have fewer fibers then.

Anyway, I wonder if cotton or cotton/polyester in a lightweight version, would be cooler.