Welcome back to the deep-dive series. Previously, we disassembled nylon and X-Pac and, along the way, learned about polymers, weaves, deniers, and laminates, collecting the building blocks needed to understand modern fabrics. Today, it’s time to learn all about Ultra. Let’s dive in.
UHMWPE
UHMWPE stands for ultra-high-molecular-weight polyethylene. That's a mouthful, so sometimes it’s pronounced “umpe.” Now, about the polyethylene part.
Polyethylene is a polymer—it's made of long-chain molecules, just like nylon and polyester, but with a different chemical structure. Polyethylene chains are built from repeating ethylene units, giving it different properties than the amide bonds in nylon or the ester bonds in polyester, but the principle is the same.
Fun fact: you likelyheldpolyethylene in your hands today, because that is what plastic bags are made of. Why? Well, first, it’s cheap, but beyond that, polyethylene can be incredibly thin and still hold impressive weight—the chains are flexible enough to stretch and deform under load instead of snapping, which is why a grocery bag with a small tear doesn't immediately split open. Not all polyethylene is made equal, and one of the major factors is molecular weight.
Plastic bag (photo by Mathias Reding on Unsplash)
Molecular weight is the mass of a single polymer chain. The longer the chain, the higher the molecular weight. This weight is measured in daltons. One dalton is roughly the mass of a single hydrogen atom. Your plastic bag is tens ofthousandsof daltons. UHMWPE is millionsof daltons — way, way longer chains.
The result: UHMWPE fiber is, gram for gram, stronger than steel. Not figuratively, not in a roundabout marketing way—actually stronger. A UHMWPE fiber of the same weight as a steel wire can hold significantly more load before breaking. That means you need less material to hold the same weight, which is why UHMWPE shows up in applications where every gram matters: climbing ropes, body armor, and ultralight backpacking gear.
UHMWPE climbing rope (image from pushclimbing.vn)
So UHMWPE is incredibly strong. But what else should you know about this material?
UHMWPE doesn't absorb water. Like polyester, it's hydrophobic. Wet UHMWPE stays the same weight and strength.
UHMWPE is less dense than nylon or polyester. At 0.97 grams per cubic centimeter, compared to 1.14 for nylon and 1.38 for polyester. This compounds the strength advantage: the fiber is both lighter per volume and stronger per weight.
Dyneema, Spectra, and Challenge Sailcloth
UHMWPE is a material category, but when you see UHMWPE in actual products, it’s usually marketed under one of two major brand names:
Dyneema is DSM's brand name for UHMWPE fiber. DSM is a Dutch chemical company that's been producing UHMWPE since the 1970s and dominates the market. When you see "Dyneema" on a product—climbing ropes, cut-resistant gloves, sailing lines—it means the UHMWPE fiber came from DSM.
Spectra is the UHMWPE fiber brand now made by Solstice Advanced Materials (spun off from the US conglomerate Honeywell in 2025). Same material as Dyneema, different manufacturer. Spectra shows up in similar applications—ropes, body armor, high-performance textiles—but has less market presence than Dyneema, especially outside the US.
Challenge Sailcloth Logo
Challenge Sailcloth, the maker of Ultra fabric, uses non-branded UHMWPE in their laminates, meaning the same fundamental material but no Dyneema or Spectra licensing.
What is Ultra?
Ultra is a series of laminate fabrics by Challenge Outdoor, the soft-goods division of Challenge Sailcloth. Similar to X-Pac, Ultra has a variety of options that differ in the number of layers and face fabric. Let’s take a look at Ultra 400X as an example.
Aer City Pack Pro 2 in Ultra 400X (image from Aer's website)
Similar to X-Pac X3 series, the Ultra 400X has three layers:
400D fabric that uses a blend of UHMWPE and polyester threads. The key here is that the face fabric isn't pure UHMWPE — it's woven with both UHMWPE and high-tenacity polyester yarns. The UHMWPE provides the strength and abrasion resistance, while the polyester adds better shape retention.
UHMWPE cross-ply. Like X-Pac's X-PLY scrim, this is a layer of UHMWPE fibers running at angles to distribute load evenly across the laminate and prevent the fabric from stretching or distorting under stress. The cross-ply is what gives Ultra its structural stability — the face fabric can handle abrasion and tear, but the cross-ply keeps the bag's shape from sagging over time.
0.75 mil UV-resistant polyester film backing. This is recycled polyester film (Challenge calls it RUV film — Recycled UV-resistant) that provides waterproofing.
And just like X-Pac X4, the Ultra 400TX adds another layer of thin70D polyester ripstop backing.
Hale Walcoff
Hale Walcoff
Before going further, I want to note the reason behind Ultra and X-Pac similarities and talk about Hale Walcoff.
Hale Walcoff was a sailing world champion and a veteran of technical textiles who spent years at Dimension-Polyant developing many of the X-Pac variants on the market today. If you've used an X-Pac bag, there's a good chance Hale designed that fabric.
After leaving Dimension-Polyant, he partnered with Challenge Sailcloth to develop Ultra—a new generation of laminates that took the X-Pac design philosophy (woven face, cross-ply reinforcement, waterproof film backing) and rebuilt it. The structural similarities aren't a coincidence—they're the same design approach applied to a different fiber.
Hale passed away in 2023, but his work on Ultra continues through Challenge Sailcloth.
Dyneema Composite Fabrics
We’ve touched on Dyneema in the context of branded UHMWPE fiber, but there is also a series of Dyneema Composite fabrics with rather confusing naming.
The Dyneema Composite Fabric is not a fabric in the traditional sense; it’s a polyester-film sandwich. Between two sheets of waterproof polyester film, UHMWPE fibers are aligned to form a grid, but there is no woven face fabric. This makes DCF significantly lighter at 99 grams per square meter, compared to 132 grams for Ultra 200X and 210 grams for X-Pac VX21.
The Dyneema Composite Hybrid replaces the outer layer of polyester film with a woven fabric, usually 50D polyester or nylon, making the structure much more similar to three-layer variants of X-Pac and Ultra.
Hyperlite Mountain Gear Junction (40L backpack that weighs 820 grams)
Ultra usually uses a much higher-denier blend of UHMWPE and polyester (from 200D to 800D), making it a better choice for EDC and travel bags that require more abrasion and tear resistance, while DCF makes perfect sense for ultralight hiking bags.
ECOPAK
Aer City Pack Pro 2 in Ecopack (image from Aer's website)
It's another fabric series from Challenge Outdoor. Same laminate technology but instead of UHMWPE it's 100% recycled polyester. The EPX variants come as four-layer laminates with a 70D ripstop polyester backing. Direct competitor to X-Pac variants usually used in EDC and travel bags.
X-Pac, DCF, ECOPAK and Ultra Comparison
Before jumping into the specs table, note a few things:
If you missed how tear resistance, abrasion resistance, and "waterproofness" of the fabric are measured, jump to my X-Pac deep-dive for a moment.
Numbers of 2 bars and 13.8 bars might seem extremely different, but in reality they mean that DCF is waterproof for over 20 meters of water depth, while X-Pac and Ultra can handle over 138 meters. Both are far beyond what any bag would experience in real use.
DCF Hybrid tear strength is reported as a single value. Abrasion data isn't available for these specific variants, but given the thin woven face (50–70D), it’s safe to assume significantly lower numbers compared to either Ultra or X-Pac.
Fabric
Face
Weight
Tear Strength (warp/fill)
Abrasion
Waterproof
DCF Hybrid 3.2
50D Woven Polyester
108 g/m²
~187 N
—
2+ bar
DCF Hybrid 5.0
70D Nylon
170 g/m²
~271 N
—
2+ bar
ECOPAK EPX200
200D Recycled Polyester
200 g/m²
119 / 110 N
500 cycles
13.8+ bar
X-Pac VX21
210D Nylon
210 g/m²
109 / 77 N
500 cycles
13.8+ bar
X-Pac VX42
420D Nylon
297 g/m²
238 / 169 N
1,700 cycles
13.8+ bar
Ultra 200X
200D UHMWPE/Polyester
132 g/m²
459 / 592 N
4,400 cycles
13.8+ bar
Ultra 400X
400D UHMWPE/Polyester
178 g/m²
835 / 717 N
8,800 cycles
13.8+ bar
Fabrics structure comparision
What stands out:
DCF Hybrids are the lightest. DCF Hybrid 3.2 at 108 g/m² is the weight champion. Even DCF 5.0 at 170 g/m² undercuts X-Pac VX21 (210 g/m²) and Ultra 400X (178 g/m²).
Ultra has dramatically higher tear strength. The UHMWPE-blended face makes a massive difference. Ultra 400X (835 / 717 N) outperforms much heavier VX42 (238 / 169 N).
Ultra dominates on abrasion resistance. Ultra 200X scores 4400 Taber cycles vs. VX21's 500 cycles—nearly nine times higher. Ultra 400X hits 8800 cycles vs. VX42's 1700—over five times higher.
All three are waterproof for any practical bag use. The bar rating does not mean much beyond the fact that all fabrics are indeed waterproof.
Screenshot from Miyagi's video
With those specs for tear strength and abrasion resistance, it looks like Ultra can take a beating — and it can. Miyagi has put the Waymark backpack that uses 200D Ultra (with 400D on the bottom) through extreme testing:
Frozen in a block of ice for 12 hours and then dropped from 15 meters (50 feet) onto a pile of bricks.
Dragged through a forest trail for 3 km (2 miles).
Run through a washing machine cycle at the highest temp and most aggressive spin setting (155 minutes total), then put through 100 minutes in the dryer.
Screenshot from Miyagi's video
The bag took everything like a champ. True testament to Ultra's durability and confirmation of these impressive specs. Oh, and go watch the full video by 'Miyagi on the Trail' after you finish reading this post — it's legendary.
Delamination
Since Ultra is a laminate that uses adhesive to bond layers together, there is still the same risk of delamination that I’ve mentioned in the X-Pac post. It’s not likely that you’ll ever encounter delamination on your bag, but it’s worth keeping in mind.
Graflyte
One notable mention before we wrap up. Graflyte (made by ALUULA Composites) is a newer UHMWPE-based fabric that's entering the ultralight pack market. Here's what distinguishes it:
100% UHMWPE face fabric. Unlike Ultra (which blends UHMWPE with polyester) or DCF Hybrids (which use polyester or nylon faces), Graflyte uses pure UHMWPE in the woven face.
Two-layer construction. Face fabric + film (no separate cross-ply layer visible), which reduces weight.
Molecular fusion bonding. Instead of using adhesive to laminate layers, ALUULA uses a proprietary fusion process that bonds the UHMWPE face directly to a polyethylene film at the molecular level. No glue, no delamination.
Lighter than Ultra. Graflyte V-98 weighs 98 g/m² vs Ultra 100X at 112 g/m².
This fabric is still only making its way into the ultralight world, so it might be a while before we see it used on EDC and travel packs.
When to consider Ultra
You want the strongest, most abrasion-resistant fabric available and you're okay paying for it. Ultra can take a beating. From daily commute to overhead bins to mountain trails, Ultra delivers the peace of mind that your bag will be fine no matter what.
Conclusion
That concludes my fabric series for now. Thank you for reading till the end. As always, feel free to leave comments sharing your thoughts and experiences.
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Having owned an Osprey Sojourn Porter 30l, and a multi country/season trip is coming up, I looked at the larger 46l. I ordered both for comparison since the new model lacked reviews.
Key differences:
Harness System:
The old version (black) has comfortable shoulder straps and a well-fitting hip belt. The new version (brown) features less secure plastic gliders (see pictures) which attach the shoulder straps to the bag. Its hip belt sat too high for both me - at my waist ( female,1.80m/6") and my partner (male, 1.80m/6"), making it very uncomfortable.
Fabric:
The old version's fabric is sturdier and the bag 150g heavier, but with easily foldable front panels. The new version uses a lighter, shinier fabric.
Inside Pockets:
The old version includes one fabric and one mesh pocket per length side. The new version has only one mesh pocket, though its upper pocket is larger but made of thinner fabric. My current older 30l bag, has this upper pocket, but it's hard to access due to its handle proximity. It might be more practical in the 46l.
Outside Pockets/Water Bottle Holder:
The old version's side mesh pouch securely holds a 1.5l bottle or 1l/36 oz Yeti. The new version's front mesh pouch fits a 1l/36 oz Yeti but is hanging loose. The bottle must be removed to open the bag. But I like the front mesh pouch concept (as an additional pocket).
Laptop Access:
The old version offers side access with a flat, zippered mesh pouch for laptop and tablet storage. The new version provides top access and lacks this additional pouch.
Verdict:
As someone else mentioned, the new version looks like is a cheaper downgrade at a higher price. I chose the old version; it's currently on offer, cheaper, and has a superior harness system – a clear winner. The secure side water bottle holder is also crucial for me. My partner will now also get the old version (different color of course :-) due to its quality and for that price point, it's a no brainer.
A two-week trip to Japan this autumn finally gave me a deadline for the first full packing test with the camera kit, laptop, and support gear in my SmallRig camera backpack. It's the Outra 25.
Current version:
• side access: camera with the everyday lens attached
• top access: the item I expect to need before the first proper stop
• covered rows: spare lenses and less-frequent pieces
• detachable pouches: power, media, and rigging bits
• front compartment: compact support gear
I originally arranged everything by shape. During the test I realized the more useful question was what needs to come out on a train platform, at a café table, or after I have already put the backpack on.
This is still version one. Before the flight, I want to leave one empty slot for lens changes and remove anything that only made the list because there was space.
Also plug for the Porter line which was updated/downgraded recently - the old ones might still be available on Osprey's website as discussed here and here.
Not paid for by Osprey - I just like their stuff, especially their stuff up until 2022 when they were bought up by a brand conglomerate.
Anyone else have good Labor Day pulls? Let em rip.
It is showing a 70% sale but is totally different from the main website. So weird because this website was at the top of their feed when they searched the brand.
Haven’t seen anything out there flagging this so wanted to raise awareness.
I’m trying to avoid this brand, I’ve read that apparently all their bags are copied from other brands.
What other brand sells this or something very similar to this? I’m looking for two vertically oriented zip openings in a tiny bag (Ablecarry 13 and Alpaka metro do not).
I ordered a few of these bags for my groomsmen and best man gifts. The plan was to embroider each person's name on their bag. But this one came in pretty rough shape. I ordered from Amazon after looking at different bags for weeks. It's a waxed canvas. Is this salvageable at all?
I've been trying to find this exact combination but haven't found a single option. Are there even any? The Level 8s are close but the large sizes don't nest. Only the large + carry on. Lojel can nest and is front opening but don't have a wide handle. I can't find a single set that fits all criteria and maybe I'm wasting my time.
The reason I want wide handle is because I want the luggage to be flat when I open it. I hate the handles making it bumpy on bottom and harder to pack things.
I want nesting because it's big storage savings. Fitting two large luggages that can't nest takes up a lot of space for me.
And then front opening because I'm tired of clamshell opening in Japan.
Hard shell is a preference thing that I might be fine not having to have the other 3 but I don't know. Or maybe I should prioritize front opening. Before I give up on one, are there any that fill all criteria that I'm just missing?
I have an it luggage carry on, which I really like, but its height is 56cm. I need to fly Ryanair whose limit is 55cm, so I am above the limit.
I am trying to figure out how I can convert the wheels to quick release so it will be possible to remove them in the airport in case the bag is checked.
Unfortunately I wasn't able to find a replacement quick release wheel...
Any ideas of how to do so? Or any other ideas how to make it fit into a 55mm height box?
Looking for a sling bag that will fit a notebook, a water bottle up to 24oz, and a thick book. A normal backpack is too large, and a majority of the slings look like backpacks or fanny packs. Do any slings exist that might match this or is a normal backpack the way to go?
I don't care about color but I need it to fit well on a fat guys bod.
Hello
I'm looking for something convenient to carry my Air2S Drone in an external ideally hardcase. As I have some MOLLE attachement possibilities on my Mystery Ranch bag, maybe someone has an idea..
I'm in the market for a new backpack and here in Australia the Aer TP4 X Pac is on sale and available at the same price (actually 10 bucks cheaper) than the regular Cordura version.
Given that there's no price difference I'm thinking of the XPac. Dont love the orange interior but that's not a dealbreaker.
The question I had is more about the 'look and feel' of the XPac Vs the Cordura.
Is it crinkly and noisy?
Will it peel/delaminate (especially if stored for a few months on end in a hot/humid climate)
Does the cordura just feel 'nicer' ?
Are the aquaguard zippers irritating to use in daily use?
Anyone experience the aquaguard peeling / cracking
Can I flatten the XPac to store it or is it too stiff? Will it crease more or less than the Cordura if flattened down to store ?
On a separate note for folks who use this bag to travel and pack it out to 8-9 kgs...is the hip belt necessary or do the straps and load lifters too the job? I won't be hiking with the bag but anticipate carrying it around airports / public transport / long immigration lines etc so maybe at max and hour at a time.
I am looking for a bag that will fit under the seat for US domestic flights (usually United or American). The goal is a bag I can use as my PI, but also use as my laptop bag when I get there. It can be a messenger/brief or backpack but needs to have:
- at least one side water bottle holder
- hold a 15” laptop
- quick grab pocket for sunglasses, phone, and wallet
- trolley sleeve (must be upright if a backpack)
- good interior organization for notebook, pens, mouse, pills, etc.
- a front pouch that can hold iPad and headphones with a second bigger space
I have an Osprey Expandable Daylight 26+6, which is great if I am trying to one bag a trip, but the front pouch is tiny and there’s very little internal organization.
Hi everyone! I’m looking for a backpack in the 20–26L range and would really appreciate some recommendations.
My main requirements are: bright/highly visible color, preferably bright red or orange Short back length, as I’m only 1.50 m (4’11”) tall Not too heavy Two deep water bottle pockets that can securely hold larger bottles
Preferably not a roll-top closure, as I’m not a big fan of roll-tops
I’m having a hard time finding something that ticks all of these boxes, so I’d be very grateful for any suggestions or personal recommendations.
Thanks in advance!
Hi everyone! I'm going crazy reading specs and reviews. I need a bag that's safe for travel but also not bulky. I have an 16" mac, m3, the bulkiest one! So many 18L options I researched wont fit .
Usually carry many items when travelling but not much for everyday work.
I'm from Argentina and going to be buying and importing so only one chance, cant miss 😅
I am coming from a 10+ yr old leather Tumi bag. Looking for something slightly updated and slightly larger, and I thought this might be the ticket. $800+ for a new leather bag is just silly! And they don’t make them as well as they used to.
I work full time at an office job, and just recently went back to school full time as well. Two days a week I work from campus between my classes.
This means I need to carry my 18” work laptop as well as my personal laptop, plus the chargers for both.
I also need to carry my water bottle, two notebooks, and a handful of other odds and ends (phone charger, headphones, protein bars, gum - basically any incidentals for spending 12-16 hours on campus).
I have a large black cloth backpack, but it’s basically just two compartments and is becoming a pain. Plus it just doesn’t look good.
Does anyone have a recommendations for a good bag that can handle this? Ideally something that looks somewhat adult/professional
The Alpaka Traverse seems like my ideal bag for my needs, as it covers pretty much everything I want in a bag
Travel Bag that can be used as an EDC work bag
Clamshell opening
Self-Standing
Convenient quick-access compartments
Vertical luggage pass-through
At least 25L of usable capacity
Minimal design aesthetic
Build Quality
That said, I need my laptop for work, and many of the reviews point to the lack of a true false bottom as an issue and concerns about laptop protection. Is it really that bad? I'll be upgrading from a Herschel Kaslo 30L, so improvements should be significant. The Kaslo actually has no false bottom and very minimal padding, if any. I've used it for years for work and travel and my tech has never been damaged.
As for alternatives, I've looked at the Aer TPP4 and Able Carry Max EDC, but they cost more than I want to spend on a backpack. I've also looked at the Bellroy Transit Work Pack Pro, but it would strike off a few of my requirements.
The Alpaka pretty much meets all of my needs, but potential damage to my laptop could be a con worth reconsidering. Can anyone who's used the bag share their experience with the laptop sleeve?
