Who makes the best clothing for Desert use

I agree with the above. I'm an exOfficio and Columbia addict…. For hiking. The stuff lasts for years with care, light colored is best, desert hats with large brims and a cloth drape on the side and neck, long sleeves and pants to stave off sunburn and reflection. The fabric gets wet with sweat but cools a lot, sometimes too much in the shade!
It's easy to keep clean and wash. Does well in thorny country.
At home I wear linen all summer, it's just cooler. But not for hiking.

Oh and I forgot REI does make some comparable pants and shirts, but they don't last as long as the exOfficio clothing.

As said it really depends as deserts tend to go to both extremes of hot and cold during 24 hours.

If your walking in 40c+ temperatures then it's going to be tough for your body to rehydrate no matter how much you drink.
The answer is to wear a few layers, that way your trapping your sweat and making each drop work as effectively as possible to cool you.

A good indication of what to wear can usually be found at looking what the locals wear.
Usually their dress has been tailored for centuries to suit their environment.

The best clothing for desert use can be very cheap. Go to a thrift store and pick up a button up shirt, athletic shorts, ball cap and bandana. Pants if you sun burn easily or need protection from brush.
Cotton works very well. Some hikers prefer synthetics in hot weather but I find them stifling and they can dehydrate you more quickly. I usually go all cotton on top, all synthetic on bottom. (cotton shirt, cotton hat, synthetic pants/shorts, synthetic underwear, synthetic socks). Moisture retention on your upper body will keep you cool while on your lower body it can cause chaffing.
Just my opinion/experiences from working summers in hot/dry weather.

There's a company called Sun Precautions that makes clothes/hats. Their "line" is called Solumbra; 100% spf fabric. Not a backpacking company per se. I've modified their full neck drape hat and like the fabric very much; big coverage, highly adjustable. Mosquito proof!

I use Railriders brand clothing. Several of their shirts have mesh lining the sides and arms as well as a rear vent. I prefer their full button shirt since I can open some of them for ventilation. Used it on the PCT in 2009 and other then some darker coloration from my backpack, its still going strong. For Pants, I like their Eco-Mesh pants which have mesh down the pant legs which does keep you legs cool. When you don't want the ventilation or walk into town, you can zip the leg and hide the mesh. I found it cool enough on the PCT that I never felt the need to change to shorts once I got out of the desert and wore them all the way to the Washington border when I finally changed them out due to it being mid-September with cooler temperatures expected for the rest of the hike.

I live in Southern California and this is the stuff I still use in the deserts. They recently came out with their similar but lighter weight Bone Flats shirt and pants, but I haven't tried them yet. Everything is rated UPF 30+. As someone who is fair skin and burns easily, I find the sun protection more than enough.

I've modified a Sunday Afternoon sun hat by attaching the Sun Precautions neck shade to the inside of the hat with velcro. Well, a tailor did this. It's kind of overkill but this combo works really well for sun and mosquitoes. I like the wide brim of the Sunday Afternoon hat much better than the baseball-brim style hat that comes with the Sun Precautions hat; but I really like the neck drape of the latter. Hence the modification.

I did the opposite. Wear a shirt with a collar, and flip up the collar during sunny hours. This is worn with a Tilley LT5B.

I live in Southern Arizona, so desert hiking is a given – I am assuming that what you're REALLY asking is "what should I wear in extreme sun/heat conditions"?

GIVEN THAT: I agree with the collared, lightweight, long-sleeved shirt idea (protects the back of the neck); I also tend to wear cotton shirts (either 100% or a 50/50 cotton/synthetic blend) for daytime, along with nylon pants (which don't get shredded by the plant life as easily). I won't even insult you by having to tell you to wear a brimmed hat! ;~) Sometimes, if I pass a water source (rare, but possible) I wet down the cotton shirt, and enjoy "air cooling" for the 15 minutes it takes to be completely dry.
No single company is going to supply all your clothes — the "rule of thumb" for desert comfort is looser, lightweight (but sun-blocking) clothes, and (although it's counter-intuitive) keep yourself well-covered (out here, tank tops & short shorts in the backcountry are signs of a rookie!). Once you follow these rules, any brand with a style/fit that you like is the right brand. And yes, one of my favorite hiking shirts actually came from a thrift shop, so money is not always a good predictor…

In my "research" I found that cotton is very often reported as not being a good sun block. I'd be curious to hear about spf values for cotton garments. My guess is that they would be very low. All of the sun shirts/pants that I know of are made out of fabrics other than cotton. However, I'd be delighted to find that I was wrong; I'd love cotton for everyday use here in sunny California!

For years I just used normal clothes such as 60/40 cotton poly. It works. No need for special clothing.

These days, since I am older and kids have left the nest, I have more expensive clothes. Also, since I don't need anything, family often buy me hiking clothes made by Ex Officio, Columbia, Patagonia, etc.

I like the Rail Rider stuff the best. So it is usually Eco Speed T or Eco-Mesh Shirt. Mostly wear Patagonia 5" Baggie shorts or sometimes Eco-Mesh trousers. The Ex Officio stuff really lasts well too.

Best bet is to go to the thrift store.

P.S. I hike hike most often in the lower Colorado/Sonoran desert, which gets a little hot each year.

I'm not a desert expert by any means, but do have some experience. I liked my light colored, long sleeved, collared button up linen shirts out there. Theoretically, i can't see why cotton-poly blends wouldn't work fine either.

I'm not sure why some people worry about the sun block protection of clothes so much, when i look rather stereo-typically Scottish of the Celtic-Highland stock (with reddish beard, light gray blue eyes, freckles and all), burn very easy, yet i don't remember a time when i got burned on my skin when that part of my skin was covered–even by.. "gasp" a pure cotton and thinnish shirt. I might not go to the desert that often, but i do frequent the beach down in southern VA plenty near Summer Solstice. Granted if i was in a Mexican desert on top of a mountain (or the like), maybe i wouldn't want a pure cotton shirt if i was going to be outside all day, but otherwise i personally wouldn't worry too much.

Cotton is generally not very good in the outdoors. Synthetic will start to stink if you get wet and don't dry out quickly or hike in it for a few days (and the smell will never go away completely no matter how much it's washed or how much bleach is used afterwards). So, I have switched to merino wool (Icebreaker).

Running shorts (synthetic), t-shirt, ball cap, bandana. For fall and spring add merino longjones, fleece sweater, rain pants, shell jacket, fleece hat, fleece gloves.

I hike in Utah. Temps can be very hot or very cold, it might rain or snow.

Cotton is great in hot weather. I get that synthetics are more comfortable because they keep you dry, but cotton is going to seriously outperform nylon or polyester in keeping you cool and preserving your body moisture. The wicking action of synthetics dehydrate you faster.

"Cotton is great in hot weather"

Just a quick correction Justin, "Cotton is great in hot, very DRY weather". But yeah, i more or less agree with the rest of your post. Linen is also great in hot dry weather, and quite good in hot and humid weather. Re: desert use, it's perhaps more useful in the sense that it will provide more insulation from the Sun, more insulation at night for warmth, and slightly better u.v. protection (if you're worried about that kind of thing).

Haven't tried this yet, but would like to next time i get out there, but wear a tighter and thinner pure cotton shirt (black colored) underneath a looser, larger pure Linen (white colored) shirt in the desert. Might maximize one's moisture for cooling, with providing more than enough u.v. protection for even the most u.v. concerned person.

I like "5.11" tactical gear in nylon for their price and quality.

But RailRiders has the most options in design and probably the best quality – but you really pay through the nose for it.

That said you can see I like tough nylon for pants for protection from our nasty Mojave vegetation. Shirts can be polyester like REI's Sahara shirts.

I've never hiked in hot weather that wasn't dry. I imagine I would feel like a soggy wet mess.
The idea of an undershirt is interesting to me. I feel like it makes me much hotter but I see many people wearing them in the summer.

It's all personal preference. If you look at the Badwater Ultramarathon, you will see some people wearing synthetics and others wearing cotton. More than just the materials, I also pay attention to the weight of the fabric. I don't like the military/tactical type stuff because I find it too heavy for my needs. I like something light and comfortable that won't chafe when covering lots of miles.

I personally wear REI Sahara pants and then some form of thin, long-sleeved, synthetic shirt. I have a 1/4 zip long sleeve jersey from Performance Bike and also a long sleeve heat gear shirt from Under Armour.

In the blazing sun, I also wear a shemagh around my neck to protect my skin and obviously a hat.