The REI Co-op Activator SI Jacket is a lightweight, slightly stretchy jacket that’s great for high activity outdoor sports. While it can shed a bit of light rain, it’s best suited for mostly dry weather and layering under a waterproof shell when the weather is truly wet.

The REI Co-op Activator SI Jacket has synthetic insulation instead of goose or duck down, which helps make this jacket more suitable for using as a layer for hard-charging skiing, snowshoeing or cold weather backpacking or hiking. Why? Lightweight synthetic jackets can resist moisture produced by your own body better than the best down jackets.

To give us a closer look, REI sent us a review unit. Here is what we learned.

REI Co-op Activator SI Jacket Review

Let’s start with the insulation. The REI Co-op Activator SI Jacket uses PrimaLoft Silver Active insulation. PrimaLoft makes some of the best synthetic insulations and originally developed its insulation for the U.S. Army, which was looking for a synthetic alternative to goose down. The results? The entire lineup of PrimaLoft tends to be heavier than high-quality goose down and it isn’t quite as warm . . . unless there is moisture involved. When goose down gets wet, its insulating properties plummet. When PrimaLoft gets wet — which takes quite a bit of water or vapor over time — it still provides a reasonably decent insulating layer.

This photo shows the inside of the REI Co-op Activator SI Jacket.

While the exterior is smooth, interior quilting holds the PrimaLoft insulation in place.

The exterior fabric on the REI Co-op Activator SI Jacket features 4-way stretch, which helps provide freedom of movement, but I must say the actual stretch is pretty slight. The cut of the jacket is regular — about average for what we see in all lightweight synthetic jackets and lightweight down jackets. Basically, if you choose your usual jacket size, you’ll have room to layer both a base layer and a fleece sweater underneath — and you will likely retain excellent overall freedom of movement.

If you want a trimmer fit, you can likely size down unless you have long arms. Still, we appreciate the slightly longer sleeve length in the Activator compared to REI’s also excellent Magma 850 down jacket: The sleeve length in the REI Co-op Activator SI Jacket in an XL men’s fits maybe 3/4 of an inch longer than the XL men’s in the REI Co-op Magma 850 Down Jacket (check out our Magma 850 review if you’re considering a down jacket).

REI Co-op Activator SI Jacket Review: Fit & Construction

What about the overall fit?

Even though I have broad shoulders — I’m about 6’3″, 220 pounds — the XL gives me good range of motion. I can get the elbows and shoulders to bind up, but only when I create artificial, conflicting arm movements. While skiing in the REI Co-op Activator SI Jacket (with a waterproof shell over it) I simply forgot I was wearing it, which means it was warm and it wasn’t annoying. I call that a win.

This image shows water beading up on the exterior of the REI Co-op Activator SI Jacket.

The DWR coating works well (but we recommend that you give all DWR a refresh as needed — we’ve had good results with Gear Aid ReviveX).

The REI Co-op Activator SI Jacket has a durable water repellant finish (DWR) that can shed a bit of light rain. Like all DWR coatings, however, it’s going to wear out and it’s not technically waterproof. If you expect to wear this jacket in the rain, it will eventually get saturated. When you pair it with a waterproof rain jacket shell, though, you get a system that can handle some bad weather and freezing temperatures very well. For instance, in single-digit Fahrenheit temperatures while skiing, I wore it as part of a layering system: a thin base layer, a fleece shirt, the Activator SI Jacket, with a shell over the top. I was plenty warm. In fact, the Activator Jacket performed equally as well as a couple of other lightweight down jackets I’ve tested in the same layering scenario. I could likely have ditched the fleece layer altogether on most ski days, but I tend to error on the side of caution when I go skiing with mixed groups of friends and family.

The two zippered hand pockets are placed a bit higher than you find on casual jackets. This lets you access the pockets when you’re wearing a backpack with a hip belt. REI also includes a single exterior chest pocket, which is plenty big enough for a smartphone, map or many two-way radios.

This image shows the drawcord on the REI Activator SI Jacket.

The drawcord seals out drafts — and is one of our must-have features for active outdoor sport jackets.

REI says the jacket weighs in at just over 16 ounces, but it’s not clear which men’s size that is. Either way, the men’s XL weighed in at almost 18 ounces. Basically, the REI Co-op Activator SI Jacket Review is a very lightweight jacket but it’s twice as heavy as a good lightweight down jacket. At the same time, the Activator SI is more robust, durable and better suited to very active sports.

REI includes an easy-to-use drawcord at the hem, which is great for sealing out drafts.

Any downsides? Not really. The REI Co-op Activator SI Jacket Review is a great jacket. Personally, I’d like to see a hooded version like the Patagonia Nano-Air Hoody (which REI also sells), but then again, if I plan on using the jacket in really cold or wet environments, I’ll have a hood on my waterproof shell anyway.

REI also makes women’s versions, along with a vest version.

REI Co-op Activator SI Jacket Review: Great Price-to-Value Ratio

All-in-all, the REI Co-op Activator SI Jacket is an excellent lightweight synthetic jacket for active outdoor sports. While its overall features and construction are competitive, it truly excels in overall value. At full price, for instance, the REI Co-op Activator SI Jacket competes well against its higher-priced competition; however, when it’s on sale, it’s an absolute steal. Highly recommended.

About The Author

Just get outside and do something. Start there. If you're already passionate about one thing, great -- start doing more things you haven't done before. Use the seasons as a guide -- winter sports in winter, bikes and motorcycles in spring, fish, camp, backpack, hike, climb, paddle in summer, hunt in the fall -- you get the idea. More kinds of experiences, not just one again and again. You'll be surprised at what you can do, what you never thought you would like, and you'll appreciate your world more than ever before. Heck, you'll be a better person -- part of Earth instead of just on it. To get a hold of me, take a "firstnamelastname" guess at

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