Layering can be hard, especially when you’re constantly starting and stopping to adjust your body temp to the environment around you. Of course, the purpose of layering and delayering has a lot to do with managing warmth - but what about sweat?

Clothes that hold onto moisture notoriously get wet, stay wet, are heavy, and ultimately can plummet the wearer’s body temperature to dangerously cold levels. Which is why we hear all the time, “cotton kills.” Sometimes, this layering game can feel like more work than the adventure itself – and we wanted to fix that.

Enter ActiveTemp™ technology: Making your apparel and accessories work smarter, so you can work harder on your objective ahead. This specialized treatment is applied to gear that you’ll want to wear when you’re most concerned about managing moisture.

ActiveTemp is a thermo-regulating polymer that dynamically works alongside your activities. When you’re exerting yourself and your temperature starts spiking, ActiveTemp reacts to that temperature increase by adjusting your microclimate to keep you cool, dry, and comfortable in a wide range of conditions.

How wide, exactly? Think of a crisp desert morning that evolves into a sunny, warm afternoon. Or a midday, uphill ski tour that ends around a bonfire. As your body experiences swings in temperature, ActiveTemp self-regulates to those changes in order to ensure complete comfort.

A climber wears a Vigor grid fleece pullover.

So, how does ActiveTemp work?

You’ve heard us use this word “polymer” a few times now. Well, ActiveTemp’s polymer has a non-Newtonian behavior, meaning its moisture affinity changes with temperature.

Yes, we’re talking about physicist Isaac Newton – and specifically, his laws of viscosity. While most other fluids become solids when chilled (think: water), ActiveTemp’s polymer does the opposite.

When we pass around vials of ActiveTemp in the office, at room temperature it’s a slow-moving gel. When they’re chilled in ice water, it becomes liquid. Warm them up in your hands for a few seconds however, and they’ll solidify.

This is the thermo-regulating part of ActiveTemp at work. Temperature affects the ability for the polymer to absorb moisture (sweat). So, it’s adjusting to your body temperature and immediate humidity levels next to skin, as you’re exerting yourself. The polymer is a liquid that keeps some moisture in, and when it’s dry, lets this out at a faster rate.

We keep saying that ActiveTemp dynamically adjusts to your temperature as things change around it, meaning its rate of moisture management is completely dependent on how you’re using – or wearing – it. It’s a sliding scale built on your own body’s microclimate.

A climber wearing a Vigor grid fleece pullover reaches into a car to unload gear.

What else should I know about ActiveTemp?

ActiveTemp is best used, and most beneficial, when worn close to skin. That’s why you’ll find it lining some of our favorite fleece styles this season – like the Trail Mix Collection and the Vigor Collection.

It’s biologically inert, meaning that its materials shouldn’t cause any interaction when coming in contact with skin. Its polymer is food grade, which means that you could technically eat it, though we would never encourage you to do that.

It’s also durable – remaining 100% effective after 40 tumbles in your washer.

Finally, ActiveTemp is bluesign® approved, meaning it’s passed a series of sustainability standards designated by the outdoor industry. Learn more about bluesign® at REI.

Where can I find it?

We incorporated ActiveTemp into a few collections that run the gamut of what this technology can do:

The Trail Mix Collection: The lightweight smart fleece that hides its thermo-regulating technology under a layer of cozy, irresistible warmth. Hiking, climbing, road tripping, cabin weekend-ing, the Trail Mix is destined to do it all.

The Vigor Collection: The thermo-regulating grid fleece that makes for a perfect midlayer, outer layer, and anytime layer for cold days in the mountains. The Vigor’s grid fleece fabric wicks sweat and allows for total breathability when you’re gunning it uphill.

The Vigor Gloves Collection:

Check out the entire technology assortment in our ActiveTemp Collection, and stay tuned for the next big breakthrough.

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