O'NEILLMen's Thermo X Long Sleeve Insulative Top

The size is just right. I like it when it sticks to the body. It doesn't bother or hinder movements. The clip for the shorts is an excellent feature. Protection against the cold is perfect for me. Before I had lycra, once wet, with the wind, it was worse than nothing at all. Often I had to stop surfing because of the cold, neck and lower back pain. Now I enjoy comfort and surf longer. I am really very happy and I recommend this article. I don't know how it will hold up over time, but it seems to be sturdy.When it's ruined, I'll buy the same one again

I've never bought a rash guard or insulative top before, but we just bought a new house with a big pool and it's just too cold outside of the summer months and too expensive to heat. I'm a bigger guy and the XL fit great. It's thick and spongy but not heavy. I had no idea what to expect. It does not constrict any movement. I kind of look cool wearing it, and even gives me a little slimming look, if I do say so myself.I can easily get into a cool pool and at first I feel just a bit of the coldness, but in 15 or 20 seconds, its great! I spend 30 to 60 minutes in the pool after 5PM and it never loses the insulating effect. It's easy to get off and it dries super quick, just letting it hang over the balcony.I'm not sending a picture, because I don't think anyone wants to see that, BUT I for sure recommend this. Saw ones that were TONS more expensive. Don't know how much better those are, but like I said this one works GREAT!!!

Own a bunch of O’Neill rashguards so naturally picked up a Thermo X for fall/winter. It’s basically what I would call a quarter mil rashguard as it’s slightly bulkier than their standard rashguards given the slightly thicker material with fleece lining. It’s thinner than 0.5mm tops though so 0.25mm seems like a fair description.No issue with movement restrictions. I wear this under a union suit that is under my dry suit for kayaking. Have been down in 20s on the water and not slightly bit cold whatsoever. Works exactly like I hoped. I have some thermal compression shirts I bought for this particular use case and picked this up afterwards. While the compression shirts are warm they sit a tad looser, nothing crazy but noticeably different fit as this sits tighter on body. But the Thermo X is definitely warmer, sometimes paying up is well worth it, this is one of those times.

I had a hard time deciding, im convinced there are no picture reviews with sizes on all of the internet. I'm 5' "8 150lbs not really muscular I went with size large, if you were muscular or slightly taller def a large, if you were my size maybe slightly smaller and wanted it to wear under a wet suit perhaps a med. I am using this for a chilly indoor water park but am very happy with the size goes past the top of my shorts plenty long enough and the connector is a cool extra and the fleece inside is very nice, soft and not too thick what you'd expect for a hat or shirt/pants to have a lining. For me I'm very happy with size and fit. Hope this helps

Very snug (as it should be), but sized as advertised. Comfortable. Quite warm in the sun. Worked well in the surf, adding a bit of warmth. Used it over a thin compression shirt for SCUBA diving in around 78-degree water. Not as warm as a wet suit, but definitely took the edge off any cold.

O'Neill has always been known for quality surf products, and their thermal does not disappoint. I have three of them for winter weather (outrigger) paddling. They support a full range of motion while keeping you toasty warm. Note: Pay attention to the sizing chart. You may want to order one size larger than normal.

This product kept me warm in a cool pool while I was training for a distance charity swim. The only time I had any trouble with it was when I accidentally wore it inside out (yes - it's easy to miss). All that fuzzy layer was on the outside providing absolutely no insulation but a ton of drag. I add this as a comical aside on an otherwise great product. The only thing I would add is that it is a bit difficult to take off when wet after a swim.

This is my first review. I just had to post something because the sizing is way off! I wear a large almost unanimously. This thing showed up and was so small I could barely get it over my head. My kids were cracking up. By the time I got it on it was so skin tight it felt like I was wearing a childs shirt and just left the Baby Gap. Again more laughter from the kids. They never have seen me in a belly shirt before.It did however fit my average sized 13 year old perfectly. And the quality looked fine, and he said it was comfortable. Just to verify it said Large on the tag.I will be returning and not ordering another one because I have no idea what size to order... 3 or 4 XL? Im skinny so Id rather just return and move on to something else. I don't want to completely discourage from someone buying as it did seem good quality and does have other good reviews. Maybe I just got a lemon....