A fleece should fit loose enough for you to fit a base layer underneath. However, it should also not be too loose because you’ll probably want to layer a jacket on top of it.
Most high-quality fleece activewear jackets are designed not to be bulky, so you can fit them underneath a shell. You'll be ready for most cold-weather pursuits with a base layer, a fleece mid-layer, and a protective shell jacket.
Fleece is relatively wind resistant. However, some kinds of fleece are better at blocking the wind than others. Most standard fleece materials don’t stop the wind entirely but block a fair amount of wind. Some fleece jackets are constructed with wind-blocking material on the exterior face. These are the most wind-resistant fleece jackets.
Fleece does not absorb much water. Though you can’t use fleece instead of a rain jacket, it will stay relatively dry in the rain. If you’re out in the rain wearing only a fleece, you will get wet whether or not the fleece material feels wet.
Some fleeces with a wind-resistant outer layer also have a DWR (durable water-repellent) coating. This DWR coating makes the wind-resistant fleece relatively waterproof, but it still shouldn’t be used in place of a rain jacket because it won’t keep you dry in a heavy downpour.
Some kinds of fleece jackets are more breathable than others. Generally, the thinner the fleece, the more air can pass through it and the more breathable it is. However, thinner fleeces won’t has as much warmth. And if something isn’t very warm, it doesn’t need to be as breathable because your body won’t build up as much heat.
Some fleece jackets are highly breathable but aren’t very warm when you stop moving. Some fleeces are less breathable but much warmer. Unfortunately, it is tough to find any jacket that is breathable enough to keep you from overheating while you’re moving and also warm enough to keep you comfortable when you stop moving. Some fleece jackets are warm and breathable but are usually more expensive.
We tested several fleece jackets that are warm and breathable. Most of our top picks were surprisingly breathable and use innovative fleece designs to accomplish this. The most breathable fleeces we tested were the Ortovox Grid Fleece Hoody, the Mountain Hardwear Kor Airshell, Patagonia R1 Air Full-zip Hoody, and The North Face Futurefleece Full-zip.