Materials

Arc’teryx used 850-fill power European goose down and synthetic Coreloft 100 insulation to augment water repellency. The two materials marry nicely, allowing the jacket to pack and carry as if 100% natural down. Coreloft is 100% polyester yarn impregnated with silicon to resist moisture absorption. In this instance, it’s used in the jacket’s shoulders and the front of the StormHood, on each side of the zipper to prevent the user’s warm breath from wetting the interior. The larger sewn squares of fabric indicate where Coreloft is used.

This jacket is not intended to provide all-weather exterior protection, however. It is designed as mid-layer or outer layer in dry, windy cold.

The insulating materials are encased in a horizontally baffled shell of Arato 10 nylon and a DWR coating, which didn’t prove as durable as other jackets in the test, requiring a small patch along the right side of the zipper. Again, keep in mind that as a midlayer, the Cerium LT (LT stands for “lightweight”) isn’t intended to be consistently pushed through dense brush or dragged through tight granite chimneys. At 10.9 ounces, the jacket’s shell and hybrid insulation combine to make a very warm, very portable puffer jacket.

Weatherproofness

The Cerium LT offers suitable but temporary protection against direct moisture. The Coreloft did its job when required, and the shell held up against brief periods of wet snow and hybrid shoulder-season precipitation mixes. One tester was surprised that the Arc’teryx StormHood wasn’t also packed with the water-resistant synthetic insulation. Still, when zipped snug, it offers an excellent seal against the elements.

The jacket’s light nylon shell surprised a tester with its ability to stop wind from penetrating the core while making lunch for guests on top of Yosemite’s Cloud’s Rest during a late fall backpacking trip, and it did the same for a slow, early morning march up the cables at Half Dome.

Temperature Control

The Cerium LT out-punches its weight class, offering exceptional warmth for a jacket that can be carried throughout the summer. The European 850-fill power goose down packed through the core, sleeves, back, and hood is the difference maker. Arc’teryx’s StormHood, which helps comfort the head and face against lower temps, adds a bonus level of temperature control, immediately helping the user gain an extra advantage against the cold.

The handwarmer pockets are small for those with bigger hands and bulky mittens, and not insulated on the interior. The drawcord around the hem has two, externally-accessed adjustment points to batten down the lower core, and elastic-banded cuffs hold the wrist nicely and showed no signs of stretch during testing.

Fit/Comfort

The jacket tested was a medium, and the primary tester is 170 pounds at 5’9’’. The Cerium LT fit precisely from sleeves to shoulders, and managed a great balance between athletic fit and room for baselayers.

The low weight factor adds to the comfort of the Cerium LT, especially when pressed under a hard-shell piece, specifically because it sustains its freedom of movement under the arms. The sleeves could stand to be hair longer, but that nitpick can be dismissed when the jacket is worn with gloves, which will protect the inch or so of reach lost when arms are extended. The adjustable hem, hood tensioning, and soft feel of the Arato nylon round out the reasons why this jacket performed so well in this rating.

Features

The Cerium LT is deliberately barebones, offering a few simple features to keep things streamlined. The dual-insulation tactic offers an added degree of protection against rain and the interior chest pocket hides a stand-alone stuff sack when it’s time to pack, making for a total of three pockets on the coat.

The StormHood has a rear adjustment point that is almost not needed given its intrinsic snug-but-not-tight fit, and when combined with the high chin zip and its Coreloft fill, makes for a dependable cold barrier. There are two hem adjusters that stayed in place when pulled taught but also may be redundant given the jacket’s natural fall-line and fit. Arc’teryx could shave an ounce or two off the coat by leaving them off. (The 2018-19 Cerium SL is only 7.6 oz.)

There are zipper garages for both handwarmer pockets and the center zip; however, the pulls are small to keep true to the “LT” spirit of the coat. Gloves make getting a clean pull a challenge at times.

The primary tester was a fan of the materials’ ratio of weight to warmth, and it’s overall approach to offering exactly what a three-season puffy jacket should: mid-layer warmth, simplicity, and reasonable protection against the elements when worn alone.