O'NEILLO'Neill Men's Thermo X Short Sleeve Insulative Top

This really works. Keeps you warm both underwater and out of the water, while being breathable and fitting like any rashguard. Not quite as warm as say 2mm neoprene but close, and its breathable, thus comfortable in and out of the water. Can be worn under neoprene wetsuits as well, for an added layer of warmth. But I've used it mostly to stay warm at the beach for body surfing etc when the temperatures aren't quite high enough to be comfortable in the water without some form of insulation, but not cold enough to require the inconvenience of a shorty wetsuit. Due to its breathability, this would also be a great safety undergarment for cold weather boating/fishing activities. Its warm and breathable and if you accidentally fall in it would provide a decent amount of insulation to help slow the onset of hypothermia.

I don't know what kind of voodoo magical material this is, but I'm glad I found it. It's like wearing a very lightweight sweatshirt in the water. Typical rash shirts are nylon and cold when you put them on, cold when you get out and the wind hits you, and can be heavy even after you've wrung the water out of them. THIS feels like a warm cloud when you first put it on and keeps me warmer than a standard rash shirt when swimming in the pool. When you take it off afterward, it is really heavy and you think, "I'm gonna need a wagon to bring this home," until you wring it out, and then, as if by some Hogwarts magic, it's lightweight and feels almost dry. I'm 5'7"", 145 lbs and got a small. It's very tight but doesn't impede movement in the water. Like a fuzzy, warm extra skin. I might have to do something crazy like buy 10 more in case they stop making them.

Definitely my new favorite water top. The outside feels similar to most rash guard material, the inside feels like a cross between microfiber and soft felt. It comes together as softer and more stretchy than rash guards or neoprene. It does not form a water tight barrier like neoprene, but restricts flow and provides better warmth and cushion than rash guards. Because it is so flexible and the inside resists sliding across the skin, It is great to reduce chaffing under the arm or around the neck when warn under a wetsuit, PFD, or BC. I bought it for whitewater kayaking and its perfect, but I can tell I will also be using it for surfing and scuba diving, both as a stand alone top and worn under a wetsuit depending on the temp. Good job O'Neill!

Seems pretty decent and warm - haven’t swum with it yet but be sure to order a size that’s large enough. For me I ordered a 2XL when the size chart said L (I had to return the XL one size up as it was super tight).

I wore this to the beach last week. This rash guard has thick, soft fabric. Not only does it provide sun protection, it also protects against some nicks and friction against surf boards and boogie boards. AND... I was surprised that I felt warming wearing it in the water vs other more basic rash guard/athletic shirts in the ocean.I like it a lot!

Excellent material and quality however, the size is way off even an extra extra large fits like a small.

Super comfy can’t wait to try it out on a full day at the lake. But make sure to get a few sizes up if you don’t like super tight things. I got a XL and I wish I would’ve tried a XXL but I’m very self conscious so a normal person would be fine.

I bought a medium and later bought a small medium fits loose once it’s wet, but the small is very difficult to get on and off. A small body doesn’t mean a small head. Neck should be made a little larger.