Millet Trilogy Sky 25+ Backpack Review

We started from the trailhead just before sunrise — headlamps on, moving at a power-hike pace toward a spring ski objective deep in Colorado’s alpine. Within an hour, the skis and skins were deployed, but the pace couldn’t let up. 

Now in the alpine, we transitioned back to boots. I slid my skis into the loops of Millet’s new Trilogy Sky 25+ backpack, unhooked my ice axe, and kept moving upward through a moderately complicated rock scramble to the summit. Perfect timing. Or as close to perfect as we’d get, given a healthy wind.

Skis on, axe stowed, BOA cinched, I dropped in. B+ turns at best, but the day’s itinerary was dialed.

The speedy little backpack on my back played a big role that day and on others like it. The Trilogy Sky 25+ is a speed mountaineering pack at heart. But it was those multi-modal days where I found its sweet spot. And that got me thinking as the last quality snow deteriorated into summer: Could this pack thrive on dusty trails, distance trail runs, and even light-and-fast overnights?

With ski season regrettably behind us, I set out to see for myself. 

In short: Millet’s Sky 25+ is a mountaineering backpack mashed together with a running vest. It sports climbing tool attachments, running vest shoulder straps, pockets for water flasks, and volume sufficient for light mountain missions. The features that make it speedy in the mountains add versatility for other fast-moving pursuits, too. It’s a surprisingly effective day hiker and even a fastpacking contender for folks dedicated to minimalist overnights. Just make sure to fill the pack’s volume for the best results — it gets floppy when half filled.

Millet Trilogy Sky 25+ Backpack Review

Millet isn’t a young brand at 104 years old. But it is recently making a comeback in the U.S. after a brief hiatus. That resurgence is accompanied by its new Alpine Trilogy lineup inspired by the classic Alps trio challenge — North Face ascents of the Grandes Jorasses, Cervin (aka Matterhorn), and the Eiger, first completed by Christophe Profit in 1985 in 24 hours.

The Trilogy series is a selection of gear designed for alpine challenges. Fortunately for all those users like me who don’t see themselves speed climbing three of the most challenging faces in the world anytime soon, the Trilogy Sky 25+ is quite versatile outside of top-level alpinism.

Backpack Layout

The Trilogy Sky 25+ is a simple foundation laced with technical features in a light package. The main fabric is incredibly strong 70D nylon with 300D Dyneema overlays for added strength and tear resistance. The fancy fabric makes the pack exceptionally tough, but it’s still just 660g. It’s also the source of the relatively high $300 price tag.

Main Body

The main pack body has essentially three pockets: one big main pocket with a cinch closure, an internal water bladder pocket, and an outer Dyneema stretch drop-in pocket. There’s also an internal Velcro pouch above the bladder sleeve. It’s a decent stash spot for small items, but it’s also prone to pulling out when digging through layers. 

Shoulder Straps

The shoulder straps are where the Trilogy Sky 25+ diverges from a typical backpack and slips into running vest territory. It fits like a running vest (more on that below). And in typical fashion, they come with soft flask holsters (flasks not included) and roomy snack pockets on each strap under the armpits.

Outer Access & Storage

The wearer’s right flank has a side access zipper that exposes a big opening into the meat of the pack. I found it super helpful for accessing layers, my buried first-aid kit, and other essentials packed toward the bottom. It’s nothing particularly innovative. But in my opinion, all top-loading packs should have one. 

I quickly stowed the long piece of cord that zigzags down the other side of the pack through anchor points. Functionally, it allows for additional storage on the outside of the pack — a foam sleeping pad, trekking poles, a rain jacket, and other relatively lightweight items come to mind. I like that the cord has its own storage slot because I found myself getting tangled in the loose string when it wasn’t storing anything. 

Mountaineering Features

Of course, Millet doesn’t shed the critical mountaineering features that you need for routes in the Alps and beyond. The dual ice tool carry is secure and elegantly integrated — maybe too elegantly. I almost missed the shaft loops on first inspection. I love this type of ice tool carry. It’s secure, yet it’s easy to grab an ice tool while you’re wearing the pack.

A very long top strap secures both the pack’s lid and a rope. It can also be used as the top attachment point for diagonal ski carry, which I’ll admit took me a while to figure out. But once it’s hooked up, the diagonal ski carry is solid enough and can accommodate a variety of ski shapes.

Diagonal carry is easily my favorite ski carry option, but it’s worth noting that the Sky 25+ does not accommodate vertical or A-frame ski carry options. 

The stretchy outer pocket is a great place to store crampons in relative security so that you don’t have to jam them into crevices around your favorite puffy inside the pack. Similarly, that pocket was a great place to stash skins to keep the wetness out of the main pocket.

The Sky 25+ does not host any dedicated avalanche tool pocket or internal loops for a shovel and probe. I ended up stashing my shovel handle and probe in the bladder pocket so they stayed up against the back panel and slid the shovel blade against the wall of the pack. That’s typically the case with dedicated mountaineering packs, so no surprises here.

Fit for Movement

It was obvious from the first time I put it on — the Trilogy Sky 25+ fits snugly on my upper body. At 6’1” and 195 pounds, I wouldn’t go smaller than the L/XL version I’ve been wearing. Even still, I couldn’t close the lower chest strap in the factory setting. But because there are easily adjustable daisy chain ladders on the shoulder straps, I bumped them up toward the top half of the straps. 

A Sneaky BOA System

It took me a few days of wearing the Sky 25+ before I fully understood the sneaky BOA fit adjustment dial. It’s located under a magnetic hatch at the bottom of the pack. The dial, which is accessible while wearing the pack, tightens the shoulder straps where they join at the lumbar.

I’ve never seen a BOA dial used like this before. While it felt gimmicky at first, I came around. It’s surprisingly effective, if slightly over-engineered. I’ve found it to be a critical pillar on which the pack’s versatility stands. 

With just a T-shirt, I crank the BOA dial down to its tightest limit for a snug, bounce-free fit. But the second I started adding layers for chillier activities, like a midlayer and a shell, I had to open the dial to release the tension and crank in the compression for just the right fit.

Is there a less technical way to design a tightening fit system like this? Most definitely. But the system on this pack is easy to adjust on the fly. It provides a fixed snugness without any bounce or elasticity. 

Weight Carry

I was impressed by how well the Sky 25+ carried weight, given that it lacks a stiff frame. As I backpacked with skis on my back, the weight felt well distributed over my shoulders and back.

That’s important because, unlike a traditional backpack, it doesn’t have a waistbelt to support the pack’s weight. Most importantly, the pack wasn’t bouncy when I was moving quickly. 

Sky 25+ Versatility

After a few visits to the French Alps, I get how mountaineers over there can get away with such small volume backpacks. There are trams, trains, and high mountain shelters all over the place. It’s heaven for fast and light mountaineering. Mountaineers and skiers don’t typically need to carry a tent or a sleeping bag for overnight itineraries. 

In Colorado’s backcountry, where long approaches are more the norm, a small alpine pack like this sees broader use, often as a hiking or scrambling pack. Could it be an overnight pack? Sure. Especially for minimalist fastpacking masochists who shun comfort and warmth in exchange for speed and distance. But don’t forget to cut your toothbrush in half to save space.

From the outset, I couldn’t help but notice that the Sky 25+ is quite similar to Outdoor Vitals’ Skyline Fastpack and MEC’s Serratus Pace UL 25 packs. Both of those packs are designed around fastpacking, or a blend of backpacking and distance running.

The shape and feature set share the critical features — running vest straps, soft flask pockets, ~25-plus-liter capacity, etc. So for the sake of comparison, I packed up the Sky 25+ with my overnight kit and bounded into the woods.

As with carrying skis, I was impressed with the comfort and poise with which the Sky+ carried the weight of minimalist lightweight overnight gear. Although there’s no elasticity built into the carrying system in favor of a sturdy platform, it wasn’t uncomfortable. I didn’t notice any pronounced chafing or fit issues after several miles. 

Millet Trilogy Sky 25+ Backpack: Limitations

The Sky+ is a worthy contender with dedicated fastpacks. The primary difference is that the Sky 25+ does not sport compression straps to cinch down the contents or compress any extra space in the pack. That isn’t a huge deal when it’s packed to the max with gear. But when it’s half full, it’s a little bit floppy. 

But it makes sense that Millet wouldn’t include outer straps on this pack, given that it’s designed for alpine climbing. It needs to be able to squeeze through rocky cracks and not get snagged in rope systems. 

Because the main pocket doesn’t cinch down, it wasn’t great for middle-distance backcountry trail running when you need to pack just an extra layer or two. The same goes for mountain biking. It was just a little too floppy for fast-moving, less gear-intensive pursuits. A dedicated running vest is still the best option there.

So, back to its core functions; the Sky 25+ is really well poised as a speedy hiker, even for adventures that don’t end up on vertical rock or ice. 

Millet Trilogy Sky 25+ Backpack: Conclusion

The Millet Trilogy Sky 25+ is an oddball backpack. It’s part running vest, part mountaineering pack. But in the right conditions, this pack works. It’s not going to replace your daily trail runner vest or your ultralight backpacking bag, but it does what it claims it will, and more in good style. 

Other than alpinists and speedy hikers, the main users that will match with this pack are light and fast backcountry skiers. It has the crucial features for all three sports — ski carry, dialed fit, gear attachments, and easily accessible water. It will even handle a fastpacking overnight if you’ve got the ultra-compact backpacking gear to fill it. You can feel secure knowing it has you covered if you find yourself speed climbing the Eiger, too.