I live in Texas. It gets hot and humid. I love the idea of a garmet that helps to cool you down. However, I found that there may be a specific performance conditon required in order to get full benefit from this garmet.How I tested it: August, 104 degrees F, 4pm. In a moving car without air conditioning, arm resting on the open window frame.How it performed for me: I was hot, sweating down my back. My back never cooled down, because there was no air circulation. The long sleeve in the cabin of the car also felt warm. However, the arm on the window did feel a bit cooler, probably due to available air flow. The best part for me was the UPF fabric. Although the sun was beating down on my arm, I never felt it. I love the longer arms length with thumb hole- I could completely cover my hands. My body was totally protected by the fabric, which is awesome, because it saves applying sunblock, then sweating it off on everything...ugh.In summary, I love the looseness and flexibility of the fabric, the UPF protection is top notch, and I Love the design with the long arms with thumb hole for extra sun protection. But I feel this would perform better with 100% air flow all around, for example when walking or hiking. So, when it heats up again, I'll test the "omni-cool" technology on different hikes in various high temps and humidity % and report back.Although not specifically designed for running, that is what I was seeking when I purchased this shirt, after much belabored research. Was looking for something that felt cool on my skin, while offering both physical and uv protection during this hot and humid stretch of NYC summer weather. I have tried many high tech wicking/cooling/uv brands and styles and they all seemed to lack the breathability and cooling effect I desperately needed to tolerate running activity in the hotter months. It must be some proprietary fabrication which combines 92% polyester and 8% elastane (spandex??) as I have worn this ratio before, but it never felt nearly as comfortable and light as this. It is truly remarkable that I can actually go out in high heat and humidity, have all the uv protection I need (although I do coat exposed areas in sunscreen, of course) and not feel unbearably hot or drenched. I also love the long sleeve hand cover for further protection, and can roll them up if I choose. And the collar is perfect in that it adds additional sun coverage, but somehow doesn't feel constricting at all. There is an welcoming, cool slinky-ness to this shirt that feels inviting even on the hottest/humid days, and has allowed me to not slack off even during the recent heat wave. I am about 5'2"/130 and got the medium which is loose and comfortable, and could easily have worn the small without it being too tight. In the summer months, I think looser is better. The fit is actually quite flattering and easy. The harbor blue is richer and more unique than most "blues" used in many popular running shirts. Plan to get other colors if/when they go on sale. This is THE BEST RUNNING SHIRT for summer -- especially for those with a low tolerance for heat/humidity/sun -- that i have ever purchased. LOVE IT!!! I suspect it will fare well into fall -- and even winter -- as well.So soft & lightweight. Neckline is flattering. It fits looser than some other Columbia Large stuff that I have so it's not clingy or fitted. The part where it looses stars is the thumb holes are in the wrong spot. When I put my thumbs thru it feels like the sleeve is twisted to the point that it is not comfortable having them on. The cuffs are thoughtfully shaped to cover the back of your hand more than the palm but the hole is in the middle of the palm. I might have kept it b/c it was a good price but since then I have found better (ex officio). I can't say if it's cooling since I didn't wear it outside but it felt nice.This shirt is not flattering on me, but it probably just be too big. I purchased a medium because they did not have smalls.The color is a bit lighter in person than in the picture. It is soft, comfortable and great for cooling in the heat. I wore it in the Serengetti for intermittently throughout a three week span and did not overheat.Very comfortable fabric with a nice drape and feel. Flattering fit and the neckline makes it more feminine and a bit dressier so that it can easily be worn with nice slacks for dinner out. Good for travel, very versatile pieceI plan to wear it to the beach in a few days! Then I'll know for sure how much I love it!I wore it to the beach and I loved it! I love the longer sleeves with the thumb slat covered my hands, and the stand up neck was perfect when I had my hair in a ponytail! I loved it , loved it!!!Great shirt! Using it as a swim shirt. Keeps me super cool and protects from the sun. Only downfall is the v-neck instead of a zipper...I'd much rather have that option. The color is beautiful too :)I do have over sensitive skin and this one did the trick and still provided some fashion color other than white. Shirt met its purpose to keep me cool and comfortable under the blazing sun with no shade.