Outdoor Research Alpine Onset Bottoms Review

The Outdoor Research Alpine Onset Merino Bottoms receive a material upgrade from the previous model. Though still a merino-blend, the design team at Outdoor Research swapped nylon fibers for Repreve recycled polyester for improved moisture wicking. They also swapped spandex for elastane jersey, making these blended bottoms even softer next-to-skin. The result is a 47% merino wool, 47% recycled polyester, 6% elastane jersey construction — an ultimate blend for comfort and performance.

Performance Comparison

Warmth

As far as lightweight bottoms go, we hardly expect these pairs of long underwear to compete in the warmth category against heavier-weight fabrics. While weight and warmth walk practically hand-in-hand when it comes to all-natural layers (i.e., 100% merino), you cannot fairly assume that a blended bottom won’t outperform its weight class when it comes to keeping you warm and cozy. Although the Alpine Onset bottoms aren’t designed for standing around an ice climbing belay, these lightweight bottoms exceeded our initial expectations for warmth.

A stealthy blend of merino wool, recycled polyester, and elastane jersey, the Alpine Onset bottoms are listed as having a fabric weight of 150 g/m², landing them firmly on the lightweight end of the spectrum when it comes to the average base layer fabric weights. So it surprised us when they tipped the scales at 6.8 ounces (for a size medium), weighing in on point with other pairs with fabric weights closer to 200 g/m². And indeed, these thin, lightweight bottoms effectively trap warm air better than expected. Layered underneath a pair of rock pants, they offer just enough warmth to cut the chill of an early-morning approach. But their ability to effectively thermoregulate truly lies in their ability to breathe.

Breathability

What these bottoms (slightly) lack in terms of warmth, they all but make up for in terms of breathability. Their light fabric weight allows for efficient airflow — like the Goldilocks zone, we never found ourselves too cold or too hot while wearing these bottoms. Utilizing the natural powers of merino wool, the Alpine Onset bottoms' ability to thermoregulate is what allows this pair of long underwear to perform so well as a multi-season layer. As you begin to work up a sweat, the merino fibers quickly wick that moisture away from your skin, efficiently passing it from the interior to the exterior of the fabric.

Even though merino is super in its own right, pairing this all-natural wonder-fiber with recycled polyester gives any base layer superpowers. Although merino wool is naturally hydrophobic, any material that is used for its wicking properties runs the risk of becoming oversaturated — once soaked, merino wool takes quite a long time to dry out. That’s where the recycled polyester comes into play, stepping up as a fast-drying fabric to offer its hand in superior moisture management. The result is an efficient-wicking, fast-drying fabric combination that quickly evaporates away moisture and allows these bottoms to breathe. Even on an all-day alpine climb in the desert Southwest — where the early-morning rain gave way to sun and 60-degree temperatures — we continued to be comfortable in the breathable Alpine Onset bottoms, even on an hours-long descent back to the trailhead.

Comfort and Fit

Breathability and comfort are truly what make the Alpine Onset bottoms such a versatile, four-season layer. While the merino wool and recycled polyester work flawlessly as a team to keep you dry and comfortable — no matter how hard you’re pushing uphill — the 6% elastane jersey is included to help bump the numbers in terms of next-to-skin comfort. While elastane is a catch-all fabric term that includes spandex, jersey knit is a technique that loops one continuous piece of yarn over itself. Imagine, for a moment, the suppleness of jersey sheets… while spandex is singularly stretchy, elastane jersey is both stretchy and incredibly soft next-to-skin.

While previous versions were defined by a next-to-skin type of fit — think thigh-hugging leggings — the re-designed Alpine Onset bottoms offer a much more forgiving cut, making them more approachable for all body shapes and sizes. For this update, the design team at OR ditched the “seamless” construction, in favor of a more classic tri-panel design, with a gusseted crotch and functional fly.

But in terms of fit, these are a far cry from a traditional pair of long underwear. Simple in appearance, but outstanding in terms of function, our favorite design point is the inclusion of two additional panels around the shins and ankles. This allows the leg to taper to a snug ankle cuff — keeping the bottoms from bunching up onto your calf — while at the same time affording more room and mobility through the thighs and knees.

Durability

Like other 150 g/m² fabric weight options, these bottoms feel almost too thin to be very dependable. Savvy consumers will notice that similar weight models — both 100% merino and full-synthetic — fall short of our durability demands. While we certainly hold products to a high standard, we firmly believe that products built with higher quality construction are ultimately more valuable. Fortunately for all involved, the Alpine Onset bottoms once again harness the capability of hybrid fabrics, and their performance extends to a level of durability altogether unexpected from this lightweight powerhouse.

Our laboratory abrasion test is designed to recreate the standard Martindale abrasion test, and vigorous rubbing over sandstone is certainly a tough way to test base layers. Amazingly, the face fabric of the Alpine Onset bottoms was practically unphased — in fact, we later had a tough time even finding the exact spot where we performed our durability test. While the flat seam construction is made more robust by flatlock seams, interestingly the seams were the spot that took the most beating in our test. However, the inner seams remained completely intact, even after repeated wash cycles. While our testing period is limited, this is surely a good indication of a long life for this pair of long underwear, regardless of how you use them.

Value

Even though these are a blended bottom, expect to pay close to 100% merino prices for this technically-advanced base layer. But the combination of performance, comfort, and durability that the Alpine Onset brings to the table all make a strong argument for the overall value of this versatile pair of lightweight long underwear. Especially for those who enjoy fast-and-light pursuits in the mountains — regardless of the season — these are a worthwhile addition to your gear closet.

Conclusion