Outdoor Vitals

CS40 Ultra Backpack

**be sure to check size charts & re-measure! (hip belts are NOT the same as for the Shadowlight Backpack)

2 Ounces. The difference between being comfortable and not.

We’ve known experienced thru-hikers that avoid some amazing remote backcountry because “the weight required for the long carries would be too uncomfortable with their frameless packs.”

So we asked ourselves, "What if we could design a frame that weighs as much as a sip of water, but could still carry all the necessary gear and weight comfortably, no matter the distance or season?"

That’s exactly what the CS40 Ultra is - the ideal 40L ultralight pack for the ultralight hiker!

It’s comfortable, durable, & stable - even if you are hiking a lot of miles all day!

And this thing is LIGHT.

There are a lot of ultralight backpacks out there that are so minimal that they aren’t even comfortable. But the CS40 Ultra was designed for extra comfort even while maintaining an ultralight weight. 

  • Comfort Redefined: Unlike other ultralight backpacks that sacrifice comfort, the CS40 Ultra prioritizes your comfort without compromising on weight. Our thoughtful design includes a full frame, functional load lifters, targeted back panel, anatomical shoulder straps, and a wide hip belt for a comfortable fit during extended hikes.
  • Ultralight Innovation: We didn't cut corners; instead, we cut weight. The secret lies in the name – CS stands for Carbon Stay. We utilized ultralight Carbon Fiber frame stays, weighing only 2 oz (combined total), to efficiently distribute your load. Functional load lifters ensure weight stays off your shoulders, making every step more comfortable. And then there's the fabric...
  • Ultra-Durable Fabric: Our Ultra fabric is as light as DCF but 6 times more abrasion-resistant and twice as strong. It ensures a tough yet lightweight pack for your adventurous pursuits. When the trail gets wild, your CS40 Ultra is up to the challenge.
  • Streamlined Design: Embrace simplicity with a minimalistic yet feature-rich design. We kept the essential features you need while eliminating unnecessary bulk. Functional load lifters, stretch mesh pockets, and ample space in the main chamber make this backpack a reliable companion.

Lightweight, durable, & streamlined  – the CS40 Ultra is the ultralight solution for hiking without sacrificing comfort.We kept all the best features you need, and got rid of the ones you don’t! 

M Torso with M Hip Belt: 27 oz


Full size, fully padded load bearing hip belt
-targeted cutouts in hip belt foam for breathability and weight reduction

Hip belt pockets with lanyard clip inside

Targeted back panel foam puts cushion where it’s most needed, and leaves voids where it’s not
-targeted cutouts for weight reduction and air movement / breathability (all for comfort)

Breathable shoulder straps with targeted cutouts and breathable ripstop mesh

Adjustable and replaceable sternum strap

Functional load lifter straps

2 carbon fiber internal frame stays

Trekking pole / ice ax retention loops

4 lashing loops on bottom panel of pack

Volumized stretch mesh pocket

Roll top closure allows additional volume

Top compression strap

3 point side compression cords

Internal hydration bladder sleeve and hydration tube port

Generously sized water bottle pockets - fit 2 bottles (smart water bottle size)


  • Volume: 51L Small Torso Size (39L main, side pockets 2L each, stretch pocket 6L, hip belt pockets 1L each)
    53L Medium & Large Torso Size (41L main, side pockets 2L each, stretch pocket 6L, hip belt pockets 1L each)
  • Main Pack Fabric: Challenge UltraWeave™ 200, - UHMWPE / high-tenacity polyester woven blend, laminated with Challenge RUV™ film
  • Hip Belt Fabric: 100D Robic™ nylon diamond ripstop
  • Dimensions: S Torso - 21.5" height (plus 10.5" roll top) x 10.75"width x 6.75" depth
    M/L Torso - 24" height (plus 10.5" roll top) x 10.75" width x 6.75" depth
  • Internal Frame: 2 carbon fiber stays
  • Zippers: YKK
  • Hardware: Duraflex plastic hardware
  • Fits up to: 40" Pant Waist
  • Max Recommended Carry Weight: 35 lbs
  • Hydration Compatible: This pack can be used with most water bladders if desired
  • Warranty: Outdoor Vitals Performance Promise

CS40 Ultra Dimensions


CS40 Ultra on the Uinta Highline Trail

Designing the CS40 Ultra Backpack

How to Properly Adjust & Fit the CS40 Ultra

CS40 Ultra Dimensions

What is UltraWeave Fabric?

Ultra 200 is a 200d laminated fabric that weighs the same as 100d fabric, but is vastly more durable (because it’s about 60% UHMWPE), with a virtually impenetrable waterproof rating (because it’s laminated with RUV film). 



Tear Strength - ATSM D2261, Warp: 103.1 lb , Fill 133.2 lb
Abrasion - ATSM 3884, 4,400 Cycles
Waterproof - 200+ PSI 

*the fabric is waterproof, however the CS40 Ultra Backpack has not been seam sealed & is thus not considered waterproof.

Ultra 200 is in the weight class of 100d Robic nylon, but has twice the tear strength and twice the abrasion resistance as 500d cordura nylon ( which weighs about 3 times as much ).

Ultra 200 Specs:
Weight - 3.5 oz/yd² , 119 gsm 


What is UHMWPE?

UHMWPE stands for Ultra High Molecular Weight Polyethylene. 

UHMWPE fibers (non-branded Dyneema® or Spectra®) are the lightest and strongest fibers commercially available, with a tensile strength 15x stronger than steel.  UHMWPE is created by a gel-spun extrusion process which draws out extremely long chains of polyethylene, aligned along a molecular backbone.  This alignment effectively transfers load through the fiber for high modulus and strength.

revolutionary fabric - featherlight frame

2 oz. That's the difference between being comfortable & not.

There's a problem with most ultralight packs

There’s a significant flaw with ultralight backpacks. They can’t carry a load comfortably.

Packs without frames tend to dig into your body and cause extra fatigue in these situations, but even ultralight packs WITH frames have major design flaws: In order to shed weight, frames are made too short or lack load lifters, failing to create the necessary angles to transfer weight to your hips, also leading to discomfort.

So we asked ourselves, "What if we could design a frame that weighs as much as a sip of water, but could still carry all the necessary gear and weight comfortably, no matter the distance or season?"

And that’s exactly what we did.

CS40 in action

Better Than Cuban Fiber Fabric or DCF

UltraWeave™ 200

It's a tight weave of UHMWPE & high-tenacity polyester that is then laminated with a non-toxic adhesive to recycled Challenge RUV™ film. Compared to DCF 150, it’s 6X more abrasion resistant and 2X stronger (tear resistance and tensile strength.)

Functional Load Lift, Unbeatable Stability

Carbon Fiber Stays

The frame stays in the CS40 Ultra are made of finely tuned carbon fiber for optimum flexibility & stability. They are tall enough for a functional load lift, and conform to your body's motion without restriction.

The best part is, you get all that extra comfort for just 2 oz!

Anatomical Design For Comfort & Breathability

Slotted Foam Padding

Targeted cutouts in the foam found on the hip belt, shoulder straps, & back panel allow the CS40 Ultra to mold with your body seamlessly while allowing for breathability.

This EVA foam will literally wrap around you without resistance!

CS40 Ultra BAckpack

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Customer Reviews

Based on 30 reviews
Angela Forester
Torres del Paine Test

I have just trialed this bag on a 7 day thru hike of Torres del Paine ( O circuit). As a smaller person; 4'10" 113lbs this bag fits well enough to be comfortable. I have a short torso and with most bags I am unable to find comfort with the frames. This bag I did not have that. But, the load can be uncomfortable if you go over the 30 -35lb mark; I found when I stuffed this bag to the max I was feeling weight on my shoulders. With that said this is an ultralight bag and if you need to carry 65 -70L then ultralight in most cases will not work.
My only real compliant is the bag is not Patagonia rain proof. The material is water resistent but after 7 hours of down pour rain the inside of the bag was wet as were some contents.


It was a great buy. Works for what I needed

Luke Brumgard
Very satisfied

So far after one hike the pack seems well made and comfortable. Looking forward to many adventures.


Fantastic backpack with a great fit!


Took it for 3 days backpacking trip carrying 32lbs feels good though I think it is its comfort limit. Integrated belt pockets are very easy to use but would be better if made waterproof. Great choice if your net load is less than 30lbs.