Arc’teryx Rho Heavyweight Zip-Neck Base Layer Assessment

Bottom Line

From our climate-controlled lab to frigid alpine starts in the Rocky Mountains, the Arc’teryx Rho Heavyweight Zip Neck base layer impressed us with its superior warmth and comfort. It’s the warmest option on our list of best base layers and the one we reach for on the year’s coldest days.

The fleece inner lining is incredibly soft, while the durable nylon exterior stands up to abrasion and easily slides under jackets. This top’s moisture-wicking is meant to keep you warm and dry, and the neck zipper lets you dump excess heat.

The Rho Heavyweight is not only practical but also looks great. We regularly wear it as a sharp fleece that says, “I like to get after it, but I also love to chill with a glass of wine.”

The Rho Heavyweight makes for an excellent base layer in the winter and mid-layer during the shoulder months, but it tends to stay at home during the hottest months, awaiting its next frigid adventure.

Comfort

Out of all the base layers we tested, the Arc’teryx Rho Heavyweight is the one we have the most trouble taking off. It’s so incredibly comfortable that we’ll wear it until we sweat.

Most of the coziness comes from the brushed inner fleece material, which is super comfortable against bare skin or layered over a t-shirt. Despite being a synthetic fiber, the polyester fleece feels like a fine rabbit’s fur.

We’re always a fan of a neck zipper, and in this case, it allows you to dial in your desired fit whether you need some extra warmth up the neck or a little more airflow and mobility. The seams are unobtrusive and are rolled down to stay out of the way of backpack straps. The fit is the perfect balance of slim yet relaxed. The arms taper down to snug wrist cuffs while the chest and shoulders are loose and roomy.

Whether layered as a base layer or a mid-layer, the Rho Heavyweight moves exactly how you want it to without bunching up or constricting. We really can’t say enough about the comfort of this base layer.

Warmth

The Rho Heavyweight is the warmest base layer that Arc’teryx makes and the warmest one we’ve tested. At 10.1 ounces, the amount of fabric alone contributes to the warmth of this base layer, but it goes much deeper than that. The Nylon exterior creates a breathable shell while the brushed Polartec fleece interior traps heat.

The neck zips up beyond the reach of a typical crew neck, extending the shirt’s warmth into critical regions. It gently hugs the bottom of your neck around vital arteries, making a huge difference in warmth retention.

The synthetic fibers on the Rho Heavyweight wick moisture surprisingly well, rivaling most wool layers. The moisture-wicking helps to keep moisture away from your body, further increasing its thermoregulation.

Because of its superior warmth, we love using the Rho Heavyweight as our first line of defense in the most arctic environments, cold nights in the tent, as well as a cozy fleece layer during shoulder seasons. It’s not the best choice for summer use or if you are planning for a highly aerobic activity and lots of perspiration.

Breathability

When subjected to our controlled drying test, the Rho Heavyweight performed surprisingly well for being such a thick base layer. It wicks moisture very efficiently to the outer layers of the garment, where it is more exposed to wind, thus speeding up drying time. The Rho Heavyweight’s drying time is comparable to that of other midweight wool and synthetic base layers.

The nylon outer material is shell-like, preventing light wind from penetrating the entire garment. Thus, we didn’t feel much of a breeze through the Rho Heavyweight. This would be a negative in an active base layer like a running shirt or sun hoodie, but because this base layer is designed to insulate, we count it as a win. Ideally, we try to avoid excess sweat build-up in cold weather. However, because of the excellent moisture wicking and less breathability of the Rho Heavyweight, sweat doesn’t cause as much of a chilling effect.

Versatility

The Arc’teryx Rho Heavyweight is specifically made for cold weather, but the beauty of it is that it works as either a base layer or a mid-layer, extending its usage. The fit is just slim enough, and the outer nylon material is slick enough to layer under a fleece layer, puffy, and/or shell. On the other hand, the fit is relaxed enough, especially with the help of the neck zipper, to comfortably fit over another base layer and even a t-shirt.

The neck zipper also extends this top’s usage into shoulder months with the ability to dump some excess heat and get a little more airflow going. 

Unlike other base layers we tested, the Rho Heavyweight comes with a handy breast pocket. The pocket easily fits a snack bar, sunglasses, and most smartphones. 

We typically reserve the Rho Heavyweight as an active base layer only in the coldest weather, and a passive insulating layer the rest of the year. It doesn’t get much use in the summertime, but if you live in a colder climate or camp at high elevations, it can definitely serve as a lightweight fleece for chilly temps.

Style

The Rho Heavyweight not only performs well, but it looks phenomenal too. We’re suckers for a good neck zipper – something about it just makes a fleece look better. The zipper lets you get so many different looks out of one shirt.

While some base layers can look a little pajama-like, the Rho Heavyweight is flattering, and you can feel confident wearing it as an outer layer for almost any occasion. The logo keeps a low profile, the arms are slim, there is just enough space in the chest and shoulders, and the waist tapers without adding too much length.

The Rho Heavyweight comes in seven different colorways, a few of which are very similar to each other. We would like to see a few more color options, but seven isn’t bad, and the colors that are offered are tasteful and understated.

Should You Buy the Arc’teryx Rho Heavyweight Zip-Neck?

The Arc’teryx Rho Heavyweight Neck Zip is ideal for someone who already has a versatile base layer or two, and wants to add something warmer to their quiver. We wouldn’t want this to be the only base layer in our closet, as it is specifically targeted towards cold weather, but it’s a solid addition.

The Rho Heavyweight outperforms most base layers when you need ultimate protection from the cold and wind, like on a serious mountaineering expedition. It effectively traps heat, wicks moisture away from your body, and dries surprisingly fast. The durable synthetic fibers will keep this base layer performing over years of heavy use.

The added features of the neck zipper and breast pocket make this layer a better all-around piece of gear. The neck zipper can be used to dump heat during aerobic activity, and the breast pocket is handy when worn as an outer or mid layer. 

Folks looking to invest in their first base layer that can be their go-to all year round might want to look into something a little more versatile. During summer months, the Rho Heavyweight is bound to see more closet time, eagerly awaiting colder weather.

What Other Base Layers Should You Consider?

REI Midweight Half Zip Review: The REI Midweight Half Zip is very similar to the Rho Heavyweight as it is synthetic, warm, and features a neck zipper, but at around half the price. The REI Midweight isn’t quite as warm but has hand thumb loops and is better for year-round usage. 

Smartwool Classic Thermal: The Classic Thermal is one of the warmest wool base layers we tested. It doesn’t have the features of the Rho Heavyweight, but it is nearly as warm and has natural odor-resistant properties.

Ortovox 185 Rock’n’wool Long Sleeve Review: The Ortovox Rock’n’Wool has the best warmth-to-weight ratio of any base layer we tested. It’s not as warm as the Rho Heavyweight, but it’s more breathable, better for aerobic activity, and warmer than most midweight base layers.