Symbiosis Aspen Female-Specific Ultralight Backpack Review

For female thru-hikers on the hunt for an ultralight backpack that actually fits their bodies, Symbiosis Gear’s Aspen pack is an exciting new option. The pack is made for people with boobs — and rather than taking the “shrink it and pink it” approach, the pack actually combines comfort with versatility.

As a female backpacker for over seven years, I’ve yet to find an ultralight pack that’s truly fit my body in every regard. I’ve battled with packs that simply don’t sit right, no matter how I pack them; shoulder straps that are too wide, causing painful chafing for days on end; sizing issues where I’ve been told to just “choose the better of the two bad options” and so much more.

I suspect that many of my fellow lady thru-hikers have also experienced the same endless search, making do with what’s out there because it’s better than the alternative.

Symbiosis Gear aims to change that, starting with their flagship product, the Aspen backpack.

Symbiosis Gear The Aspen Ultralight Backpack

Loaded up and ready to go! The Aspen in action on a weekend backpacking trip in Moab.

Symbiosis Gear Aspen At a Glance

MSRP: $299
Capacity: 38L
Weight: 25 oz
Sizes: One size fits many; best for women 5’2″ to 5’10” with bust sizes A to DDD, but can be worn outside of that range
Materials: 420D Extreema and Spandura UHMWPE

Circumstances of Review

I’m a 5’5″ woman with an average-sized bust, and I had no issues dialing in my fit on this pack. I tested the Aspen on a backpacking trip in Canyonlands National Park, where I carried up to 25 pounds and hiked across terrain that required a lot of mobility: scrambling, climbing, and generally more vertical movement than a typical thru-hike would require.

I also tested this backpack with 15 and 20 pounds on various day hikes around Colorado’s front country.

Intended Use

The Aspen is a minimalist, ultralight backpacking pack designed for multi-day trips. Plainly put, this pack is tailor-made for people with boobs (this literally is the company’s slogan) and fits women of varying body shapes and sizes. It’s niche, it’s specific, and it’s designed for female thru-hikers and backpackers wanting a frameless, ultralight pack that fits.

Those with an lightweight or ultralight gear setup will get the most from this pack. The company suggests it’s best for backpackers with a base weight of around 10 pounds, and maxes out at a total load of 20 pounds.

That said, I do think you can stretch the 20-pound limit. I carried up to 25 pounds in the Aspen and was surprised by how comfortable it was over a weekend of backpacking.


The Aspen features S-shaped shoulder straps, an accessible phone pocket, and stretchy adjustable sternum strap with a cushioned back panel

Boob-Friendly S-Curve Straps

Traditional backpack straps often cause discomfort and chafing and are often too straight or wide to fit a woman’s chest. The S-curved shoulder straps seamlessly accommodated the natural contour of my body, distributing weight more evenly and reducing pressure points.

3-Way Adjustable Sternum Strap

One of the most unique aspects of the pack, the Aspen’s three-way adjustability and stretchy sternum strap allow for a customized fit that accommodates a wide range of bust sizes and shapes.

With traditional sternum straps that have no elastic built in, I often feel like my breathing can become restricted with pressure on my chest. Yet the stretchy strap on this pack made it easy to adjust when adding or taking off layers, improving overall comfort regardless of the user’s body type.

Holster Phone Pocket

In today’s digital age, having quick access to essential items such as your phone is crucial, even on trail. The Aspen’s easy-access phone pocket is stowed on the shoulder strap, providing storage space for phones or other small essentials, like snacks, sunglasses, or lip balm, without disrupting the flow of a hike.

Adjustable Hip Belt

This pack has a wide, non-load bearing waist belt that can be stowed away to increase mobility around the hips. I was skeptical of this feature at first, as my personal preference is to carry the brunt of my pack’s weight on my hips, but I was pleasantly surprised by the belt’s functionality.

Since the upper portion of the pack fit significantly better than most I’ve tried, I felt more comfortable distributing more weight to my shoulders, thus freeing up my lower body to scramble and climb with ease.

The non-load bearing hip belt made scrambling up and over slot canyons a breeze, with full range of mobility in my legs and hips.

Functional Pockets

Symbiosis Gear is dispelling the myth that women’s gear and apparel should only have fashionable, not functional, pockets. In addition to a large, durable back pocket with zigzag compression straps to stow gear away on the outside of the pack, the Aspen boasts two extra-large side pockets with shock cords to tighten if needed.

I was able to carry two Smartwater bottles and a filter in just one pocket. The pack also has a stealth bottom pocket, perfect for housing your sit pad, map, or additional layer.

Intentional Features

Although it’s a pretty minimal setup, as most ultralight backpacks are, it would be remiss not to mention the intentional features that made everyday use so convenient. The pack features a Y-strap and roll-top closure, allowing for optimal versatility and capacity when packing.

The pack is mainly crafted out of 420D Extreema, assuring thru-hikers of its ability to withstand rugged terrain, tough-on-gear thru-hikes, and water resistance. It even included an adjustable ice axe and trekking pole loop.

Y-strap and roll-top closure on the Aspen make the pack highly versatile

Women’s vs. Men’s/Unisex Backpacks

Is there really a difference between a backpack for a female vs. male hiker? The answer is a resounding yes. While backpack fit is often personal preference, some key features can account for female physiology when crafting an ideal backpack, particularly concerning fit and comfort.

Typically, women’s packs have a shorter torso range, include shoulder straps that are more narrow and shorter in design, and have narrower, flared hip belts that are more load-bearing since our center of gravity sits lowers in the hips.

S-curve straps, which the Aspen does feature, are not actually the defining element of this pack; many other female-specific backpacks incorporate this design. Instead, it’s the Aspen’s S-curve straps coupled with the fit and stretchy sternum strap that really made it fit like a dream for me. The pack sat perfectly on my mid-lower back, felt comfortable on my shoulders with no dead space, hugged my body, and was adjustable from nearly every fit standpoint.

The concept of a female-specific pack isn’t new, but an ultralight pack that’s specifically designed for female bodies? Now that’s something I’ve struggled to find a cogent version of.

Hyperlite Mountain Gear and Gossamer Gear ultralight packs are typically “unisex,” but what that really means is that it will work better for some and not others. As a former HMG wearer, I typically found myself between sizes or dealing with the inevitability of a pack sitting too high on my back.

Frameless vs. Framed Packs

Frameless packs like the Aspen are characterized by their lightweight design and minimalist construction. They’re ultralight because the lack of a frame removes a significant amount of weight. They tend to be less expensive (but you can often make up the cost in ultralight materials like Dyneema), offer less carrying capacity, and do not include much built-in ventilation, since the pack sits directly on your back.

A frameless pack also may have a more forgiving fit, as a less rigid back panel can be more flexible with torso sizing, which is usually where the unisex label comes in.

A framed pack can either have an external or internal frame, allowing you to carry more weight due to a stronger structure. These packs are known for ventilated back panels that keep your sweat from pooling, are heavier in nature, and usually feature an adjustable torso.

While frameless packs are certainly not everyone’s cup of tea, the Aspen’s frameless design prioritizes agility and efficiency on trail. Yet it doesn’t sacrifice the comfort as much as many other ultralight packs do, with more cushioning in the back panel and shoulder straps.

Symbiosis Gear Aspen Ultralight Backpack Pros

All-Day Comfort

The Aspen is by far the most comfortable frameless backpack I’ve ever worn. I was pleasantly surprised at how well it contours every inch of my body, from the way it hugs my shoulders to where it sits on my back. There are seemingly endless adjustment points, from the stretchy sternum strap that can be moved on a daisy chain going all the way down the shoulder straps, to a lengthy hip belt and shoulder straps.

With other ultralight packs I’ve used, I’ve often had to take breaks, giving my weary shoulders a rest if I’ve pushed the weight capacity. With the Aspen, I felt no major difference in the way it carried with an additional five pounds over the recommended weight limit.

The face of pure happiness because my pack finally fits. After two days of long miles and scrambling, my shoulders and back hardly felt it due to the Aspen’s comfortable fit.

Stretchy Sternum Strap

I’ve tried packs with adjustable sternum straps before that move vertically along the pack’s shoulder straps, but never one with horizontal stretch. It was a game changer, and I’m never going back. My breathing didn’t feel restricted, and it made adjusting the sternum strap seamless based on the layers I was wearing.

This is an ideal feature for women with larger bust sizes, as there is plenty of room for adjustment.

Gigantic Side Pockets

The side pockets on this pack were almost comically large, but Symbiosis Gear thought of everything, including shock cord to tighten the side pockets as needed. I easily fit two Smartwater bottles in one pocket, plus a water filter and snacks.

Although the pack is only listed as 38 liters, the side pockets added many opportunities to holster easy-access items. Plus, it was astronomically easier to reach back and grab my waters without taking my backpack off, something I really appreciated when I was grinding to make miles without stopping.

Extra storage space galore! These gigantic pockets were adjustable with shock cord.

S-Curve Straps

This goes without saying, but the S-curve straps contributed greatly to the quintessential fit of this pack. They prevented chafing on my arms, and allowed the backpack to sit comfortably.

Mobility of Hip Belt

To be transparent, I actually thought I’d hate the non-weight bearing hip belt. As I mentioned above, I actually prefer to carry more of my weight on my hips, so I was worried this wouldn’t be the pack for me.

Let me be the first to admit that the Aspen changed me. The waist belt straps are thick enough that they don’t feel like they’re cutting into your skin, and they’re so comfortable and light that you’ll forget they’re there. I enjoyed the high range of mobility that came with the hip belt, especially when scrambling up and over fallen trees or climbing slick rock in Moab.

Symbiosis Gear Aspen Cons

Compression Straps Too Short

The biggest oversight, and one that would be an easy DIY fix, was the length of the zigzag compression straps on the back of this pack being too short. I was excited to utilize this feature, as I typically stash my bathroom products, first aid kid, camp shoes, and an extra layer on the back of my pack.

However, unless my backpack was only packed half-full, the zigzag compression straps became too tight to use, making it impossible to access the back pocket as well.

This is something I could easily replace myself (and probably will). But, I was a bit disappointed I couldn’t use the back pocket and compression straps at all when my backpack was stuffed normally.

Since the zigzag compression straps were too short, it rendered the back pocket (and straps themselves) pretty useless. I was able to just barely stuff my camp shoes in there when partially packed.

Open Phone Pocket

While the front phone pocket was overall incredibly convenient, it was just small enough that I was worried my phone might topple out when scrambling or crossing rivers.

If you’re on trail where there’s not much dynamic movement other than vertical walking, this would be a moot point, so take it with a grain of salt. But if you’re trekking on something like the Hayduke or Sierra High Route, I’d suggest a more secure phone pocket.

Limited Sizing Options

Since this pack really is one- size-fits-many, it is limited to women (or men with a narrow frame). Selfishly, this wasn’t a con for me. I’m a hiker with boobs, I’ve never had a backpack fit me 100 percent, and I was ecstatic to find a female-specific pack that was intentionally designed with my body type in mind.

However, if you’re a man wondering why this pack wasn’t made for you or a woman significantly shorter than 5’2 or taller than 5’10, it’s possible the pack may not fit as comfortably, despite its well-thought out features. That said, there are lots of other great packs for men, so I’ll enjoy this specialized pack with no qualms.

Limited to Ultralighters

Because of the lower carrying capacity, this pack is mainly ideal for folks with an ultralight setup. Although it maxes out around 20 pounds, I could comfortably carry over that range. If you have a base weight that’s significantly higher than 10 pounds, this pack may not be for you. After all, it is frameless, ultralight, and 38 liters.

Overall Value

The Symbiosis Gear Aspen ultralight backpack offers exceptional value for female backpackers seeking comfort, functionality, and performance on the trail. Its innovative design, tailored fit, and premium materials make it a standout choice in the ultralight backpacking market, specifically catering to the pain points that female backpackers often face with gear.

As a women with boobs who’s been searching for a pack that truly fits since, well, the first day I ever bought a backpack seven years ago, I’m thrilled to have found an option for short weekend trips that will make its way into my gear rotation.

With a commitment to inclusivity and comfort, Symbiosis Gear has successfully elevated the backpacking experience for women, paving the way for more inclusive and user-centric gear solutions.

Shop the Symbiosis Aspen Backpack

Comparable Packs

Granite Gear Perimeter 35 Women’s Fit

  • MSRP: $229.95
  • Weight: 3 lbs

Osprey Eja 38L Women’s

  • MSRP: $220
  • Weight: 2.5 lbs

The Symbiosis Aspen ultralight backpack was donated for purpose of review

Affiliate Disclosure

This website contains affiliate links, which means The Trek may receive a percentage of any product or service you purchase using the links in the articles or advertisements. The buyer pays the same price as they would otherwise, and your purchase helps to support The Trek's ongoing goal to serve you quality backpacking advice and information. Thanks for your support!

To learn more, please visit the About This Site page.

What Do You Think?