Essentially my favourite mid-layer for all the seasons, but personally I liked the Flash version better. This one is light and stretchy enough for climbing, biking, or just hiking around the trail. It packs down small for keeping in your pack. The pocket is pretty useful for most things, like an iPod, or camera. But it is also warm enough to ski in, not binding your movements, and not overheating you on the hike up. The checkered pattern of the Regulator fleece is really nice, it reduces the weight and bulk, while keeping you warm and mobile. The only thing that this fleece is not good for is wind, just cuts right through the fabric and into you. The Flash had nice stretch panels that made it more useful for all these applications, but this is good for full coverage fleece. Definitely liked the offset zipper of the Flash better than the straight one, because anyone who has ever got a zipper frozen to their lip knows, offset is a nice feature for no extra weight.

This is my go to layer for high-speed winter pursuits. Works great as a light fleece for the summer/shoulder seasons as well, and is super compressible to boot. Good for backpacking, good for wearing to class...All in all an extremely versatile and comfortable layer. If you're looking for sheer warmth, go up a weight or two, but for all around performance and breathability this piece is a good choice.

This is one of my all time favorite pieces of clothing. It can be used is such a wide variety of situations, cold weather as a layer, or cool spring/fall as an outer layer. The checked fabric keeps the right amount of heat in when it's needed, but breathes well when its warmer. If you buy one, make sure you buy a second in another color because you'll love it that much.

If you only own one piece of outdoor gear, this should be it. I wear mine for everything - from warming up in a chilly office to skiing to mountaineering to running. It's almost magic, the perfect layer.

Great weight for those days when there's a nip in the air. Light, easy to move in. I wear it to play golf on those early fall mornings.

This jacket works great as a heavy insulation layer in COLD weather, it is thin and fit well under most shells. I would not recommend it for wearing under a thin rain jacket, rather under a heavier waterproof ski-like jacket. The R1 also wears great on its own for those cool summer nights, where the temps don't call for a full blown fleece. The sizing runs True I'm 6'1" 220 and an XL fits me perfect. I high recommend this jacket.

I am 6'4" and wear an XL in patagonia. Great top, I have the hooded version but the same basics apply. It can be worn against the skin or over a capilene. Smooth outer surface makes adding a layer on top of it easier because it does not cling as much as a normal fleece. Wish I had had this piece of gear on my NOLS trip. One of the most versatile layers I have seen.

Super breathable, super stretchy, and super comfy. It has a long cut for snow-beating security, and just great fit for us lanky gents. On top of that, Patagonia is one of the most customer-friendly businesses around; if at any time you decide you don't like your product, you can return it no questions asked. My advice? Buy two: one to sweat in and get dirty, and the other for swanky around town wear. Also, bonus for getting rid of the offset zipper, which I didn't like so much.

Quality fleece. Great for cool temperatures or winter runs.

this is the best layering piece I've ever owned! I wear this top at least 3 to 5 times a week for about 8 months. It is my go to piece for skiing, fishing, climbing, whatever.

I consider this my workhorse layer. It comes with me during day hikes in the summer, aggressive ski days in the winter, and slogs through the winter snow in the adirondacks. There is nothing the R1 fleece can't do.