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)

Colored white for reduction in heat on contents


  • 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
  • Pack 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
    (scroll down for hip belt dimensions)
  • 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

Pack 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

Hip Belt Dimensions (not including webbing):

  • XS - 25.5" length, pockets 4.75" x 2"
  • S - 27.25” length, pockets 5.5" x 2”
  • M - 30” length, pockets 6.5" x 2”
  • L - 34” length, pockets 6.5" x 2”
  • XL - 36.25” length, pockets 6.5" x 2”


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 36 reviews

Loved everything about this pack except one thing.

Pros: very light, carbon frame is fantastic, very comfortable (as long as you don’t overload it), water bottle pockets were deep and accessible while hiking, load lifters were a life saver.

Cons: bear vault (475) would not fit in on its side. I had to stand it up.

Slick Pack for sure

Went with the CS-40 as a replacement for another brand as Lightweight is Super important for my Nerve Damage. I def need to learn to pack it. It doesn’t seem as wide(from back to front ways as my others and that is interesting for sure to me. Can’t wait to use it on my CT thru-hike this year. But my base weight of basic 4 needs is 9.2lbs. Happy Veteran here.

Thomas Doyle
This Was a Gift

I bought the backpack for my som. He says that he likes the pack especially the weight of it.


Great backpack! Feels comfortable. Like the fact you can change sizes of hip belt.

Linda Galt Powley
Light, durable, worth the price

Bought it to replace my first grey Outdoor Vital backpack. The original walked Camino Frances with me in 2018. This lovely pack completed the 800 KM Camino Frances in 2023. It was large enough to store my spare set of clothes, food and water for most of the day. I learned in 2018 reservoir water containers are not the best, bottles are and this pack carried my 2 liters without problem. Lots of compliments, unusual due to the classy white and black! I used a wp pack liter and light weight backs to separate clothes, other gear. Couldn't be happier. I carried my pack throughout the trail, no aches or pains. Tried Osprey, on the West Highland way and Great Glen way, Was not balanced for me. This pack worked wonders and I hope to schedule another hiking trip soon to use the pack again. Mahalo for your hard work.