temperature above which you wouldn’t hike in merino

I generally wear my light-colored long sleeve lightweight merino shirt in mid to high 70s with the sleeves rolled up and the chest zip nearly all the way down. The icebreaker chest zippers are way too short, in my opinion.

I doubt synthetic would have made a big difference. You were in a black long-sleeve shirt in 80 degree weather in the sun. No wonder you were sweating. Color makes a big difference, as does lack of venting.

At a certain point, nothing beats the feel of cotton on a hot day. Wether that is a t-shirt or a button up of some sort. Merino and synthetic end up feeling like clammy hot greenhouses.

Chrome dome.

After years of noticing that BPers carrying umbrellas were amount the most experienced, I took the plunge.

I felt 10-15F cooler.

But, yeah, I'd have been in white polypropylene or a loose cotton retired dress shirt if there was chance of rain.

I hike in an Ibex 150 weight Merino long sleeve shirt in all temperatures. It's light grey. Most of my hiking is in the Southern CA mountains. It's often exposed, sunny and quite hot. I've not had any issues in wool and it protects great from sunburn. In a blue poly shirt I wore a number of times I found the shirt material made me sweat more. Also, when exposed to wind I chilled quickly which doesn't happen in the wool shirt. I would try a lighter colour in wool or as others mentioned cotton.

I just wore my BPL merino hoody in the Grand Canyon in April- I wanted sleeves for sun protection. It was 90F. I had no problems- if I was sweating a lot it must have been evaporating pretty quick because I was pretty comfortable. (Certainly more comfortable than I would have been with a sunburn…)

Lightweight merino or merino/poly blend irrespective of weather for me- when it's seriously hot and dry, threadbare cotton is my go to material.

I haven't had much luck with 100% nylon or poly garments, especially in direct sun and heat, Capilene 2 being the exception- that material is a wonder fabric thanks to the weave Patagonia uses. I soak out my back wearing merino, even in cool conditions, but I don't mind it one bit. A damp merino shirt feels significantly more comfortable on my skin than a saturated synthetic number.

The texture, weight, and knit pattern is equally as important as the material, having owned a few merino hoodies I have learned that not all hoodies are equal despite equivalent fabric weights and material. My old BPL Beartooth Hoody was fine into the 80's, the material was thin and handled the broadest range of temperatures of any garment I can think of.

Consider a thin merino/poly blend for hotter days, and when its really hot and dry (90's-100's) don't rule out a simple cotton shirt.

I use the same long sleeved Merino Woolnet shirt four seasons (Aclima Woolnet); in the winter at -25C and in the summer +25C and above. In the winter I usually wear a shell jacket over the Woolnet and a down sweater on top of that when I take a break.

My previous walking shirt was a light coloured 150wt merino LS shirt (Smartwool Microweight) This worked very well in the heat.

Around Xmas time I swapped this out for a Rab Meco 120 LS shirt. It's amazing. The merino/poly blend really dries quicker and the evaporative colling feels great.

I'm an Aussie and we get plenty of hot humid weather but maybe we are a little more used to it ??. After using the 150wt and now the Meco LS shirts I'll never change back to anything. Even in 40°C (104°F) weather the Meco is the coolest feeling shirt I have worn.

What type of pack did you have on ?? Does the back breath much. I find a big body temperature difference when swapping between my osprey exos (vented back) and golite jam 2 (No venting, just pack straight against your back)

Personal preference.
I pretty much always have a short sleeve Merino T as my first layer (140 or 190) even in 100f weather because I don't sweat very much (nor drink very much…) and like the feel and lack of smell of them.
(at around 100f I will likely have an open thin long sleeve shirt on top…)
Franco

Above 75 I would go straight to cotton, unless I am in an area where the weather could change quickly and get cold.

Thanks everyone.

I guess my color choice of black was unfortunate. I never considered cotton since my past experiences always left me very wet and I'm reluctant to pack an extra shirt for extremely warm temperatures. The merino/poly blends also sound interesting. Beyond the RAB, are there other long sleeve blends to choose from? The Patagonia blend has an overly slim cut for me.

Thanks again.

rhz

I've worn my Merino 1 crew comfortably into the 80's- thankfully it doesn't get much warmer than that in the mountains :) Mine is an older style, not sure what changes they've made w/ the new one- it's a little trim, but I find all base layers on the trim side

the ~ 65/35 blend is just about perfect IMO

I agree with mike that the patagonia merino/synth blend is the way to go in warm weather. FWIW I wore a a couple pure merino T-shirts for three months strait in sumatra (on the equator) and it was fine. The problem with cotton in the heat is that once you sweat it out it it wont breath or wick so it ends up feeling hotter. Cotton and backpacking dont really go together regardless of the season.

I hike in Maryland / Virginia where it's 90-105° F with 80-90% humidity. I find loose fitting thin poly T-shirts feel lots cooler than cotton because the moisture evaporates so fast. I think wool is on the middle, but closer to poly in the lighter weights. Nylon is usually thicker, and is worse than cotton for low exertion times, but better than cotton for medium and higher exertion times.

On long trips where there is a possibility of sudden cold wet rain/hail, I go with a light colored lightweight merino blend or vented synthetic RailRyders type shirt.

Many high elevations locations can have temps ranging from 100 f, but can blow hypothermia inducing cold rain/snow/sleet in August. If I'm only carrying one shirt, I don't want it to be cotton.

Last weekend, I spent both days outdoors fully exposed to sun at 95+ degrees and switched shirts as a test and found no appreciable difference in comfort between equivalent nylon, cotton and merino shirts.

I was surprised how cool the merino was, but I have found it is also the flimsiest when made that light weight. Nylon is smelly, but much more durable.

Cotton is usually the least expensive option. Not as durable as nylon, but more durable than merino.

@ John – You feel cooler in hot temperatures when moisture is quickly removed? Try hiking with an absorbent material like cotton again and report back on whether you are hotter or cooler in these blistering hot temperatures with slightly damp clothing. You should be cooler. The adage of "cotton kills" is principally for those hiking in cooler climates where a wicking material is critical to retaining body warmth. Being wet, even if slightly, should cool you down. Similarly, if you ever fall in a lake and it is cold outside, take off all your clothing immediately as you'll be warmer without clothes than with wet clothing still on.

"Similarly, if you ever fall in a lake and it is cold outside, take off all your clothing immediately as you'll be warmer without clothes than with wet clothing still on."

I thought this only applied to cotton clothing. If you fell into a lake with polyester and/or wool clothing, after you started moving and getting warmth pumping, wouldn't you be warmer with that clothing still on? I figured that wet cotton has a negative insulative effect while polyester loses a lot of it's insulative value but not all of it. I have also experienced wool clothing being warm even when soaking wet, more so than polyester.