NRS Hydroskin Rash Guard - Short-Sleeve - Men's - 2007 BCS

I've used the Hydroskin for two situations:

1) teaching students to roll their kayaks in an extended pool session (as well as demonstrating some rolls myself)
2) snorkeling in Hawaii in water that wasn't quite warm enough to stay in for long

In both cases, I would have been fine in the water for a short time, but the Hydroskin allowed me to keep warm for an extended time in the water.

I like the flexibility (all kinds of rolls were easy, with no hindrance in freedom of motion). The Hydroskin is also easier to take off than the previous Lotus rashguard I had ... because it isn't so "sticky" when wet.

The only issue has been that some of the stitching is not as durable as I'd like ... I've had a few loose ends where the stitching has unraveled (but nothing that compromises the integrity of the shirt).

There's only one kind of weather/water temp condition that I would want the short sleeve top for: Really hot weather, and really cold water. Like if you do a lot of kayaking on dam-released rivers in the hot summer months, this would probably be better than the long sleeve version.
However, I've usually found that if I'm wearing hydroskin, it's because I want to be really warm. And if I want to be warm, I want my whole upper body covered (without half of my arms exposed). So if you're cold water/cold weather boating, go for the long sleeve version.