The bottom line: The Icebreaker 260 Zone Half Zip Hood is a warm Merino hooded baselayer suitable for just about any outdoor activity in the cold.
The Icebreaker 260 Zone is a Merino wool long-sleeve baselayer intended for use in cooler temperatures. The shirt is made of 97% Merino wool at 260g/m^2, which is somewhat thick. At 12.52 oz, it's not the lightest baselayer top - however, it is one of the warmest due to the type, quality, and weight of the fabric.
This review discusses the Half Zip Hood, but the 260 Zone also comes in a crewe neck and a non-hooded half zip.
The 260 Zone is incredibly warm and comfortable. We just got our first 28F morning of the year a few weeks ago here in New York, and I went out on a run with the 260 Zone as my only top layer. I was comfortably warm, though it was a bit chilly when the wind came through.
At 12.52 oz, this shirt is not quite the lightest baselayer you'll find, but the warmth-to-weight ratio is fantastic. Icebreaker call this shirt "midweight," and intend the shirt to be used on chillier or windier days. It breathes exceptionally well, so you won't sweat through it as easily, even when it's warmer out. If you do sweat through the shirt, the Merino wool stays warm longer and doesn't feel as gross or clammy. Icebreaker also claim that this shirt is odor-resistant, which I seriously doubted. But it actually is - even after sweaty runs, this shirt doesn't stink, which is pretty awesome. Also - this shirt is so soft. It just feels great to wear.
The zipper on the half zip is pretty long, which makes it useful for temperature regulation when during exercise, although it feels a bit awkward when unzipped all the way. The sleeves have thumb holes, which are comfortable - although the sleeves are quite long (see below). Overall the shirt feels high-quality and very durable, and I expect it to last many years.
The shirt also has "heat dumping zones" under the armpits and on the back that are meant to be cooler and more breathable, to keep you from sweating through the shirt so quickly. The material in these areas is slightly thinner and has a different, looser knit. For really active sports like running where you're generating lots of heat and sweat, this is really useful. However, the downside is that if you're hiking on a windy day, the extra breathability lets the wind right through the shirt, and cools you down quickly. Overall though the shirt is quite warm, and especially if combined with a windproof shell it makes the perfect baselayer for pretty much any cold-weather activity.
Let's talk about the fit for a minute - because it's a bit weird. Icebreaker apparently use a very slim fit, because the shirts are tight with extra long arms. I am about 6 feet tall, 165 pounds, and I ordered a medium, which fits great for me around the torso, although the arms are somehow still a bit long on me. Icebreaker offer a "Fit Finder" on their website, which worked out well for me, and I'd recommend using it before buying. For shorter folks or those who don't want a super tight fit, you might find the 260 Zone to be a bit too long in the arms.
At between $120-140 for the three styles, it doesn't come cheap - but you're paying for the best quality. And compared to similar Merino shirts, it's pretty similar in price. If you can find one that fits you, I strongly recommend the Icebreaker 260 Zone. It's a comfortable, durable, and warm shirt suitable for just about any cold-weather activity.