Nov 4, 2010 at 3:42 pm #1265149
I know I've seen it posted somewhere, but I can't seem to find how to decipher Cuben fiber product codes. Does anybody here know the secret?
Over a year ago, I bought some pretty heavy bias fiber Cuben (CT9HBK.18)to make a pack for a try at thru-hiking the AT. Then I ended up having a job for a year long than expected, so I haven't sewn with it yet. It IS very heavy, 78g/m2, but it should hold up well to sewing, and I tend to fall down a lot, so I'm OK with the extra weight.
I bought an entire 9meter panel, 51 inches wide, so I will have some left over after I make the pack, if anyone is interested.
I also have a question about shoulder strap placement. I prefer to take as much pack weight on my hips as possible, so when I'm using a pack with load lifters, I crank the hipbelt and use the loadlifters to keep the straps elevated off my shoulders. So–couldn't I just mount the upper ends of the shoulder straps "too high", that is, where the load lifters would normally attach, and get the same effect more simply? (My gear at this point is pretty light, and I expect to come in under 20lbs, possibly under 17, and the pack will have a corrugated plastic sheet in it, like the old GoLite Infinity, with the stuffable straps of a GG Mariposa.)
So if I am looking at this the wrong way, somebody please tell me–I'll be taking an exacto knife to the Cuben pretty soon. ThanksNov 4, 2010 at 3:55 pm #1661166
eric chanBPL Member
is this what yr looking for?Nov 4, 2010 at 4:00 pm #1661168
CT = Cubic Tech, the manufacturer
9HBK = Tells you how much spectra (9K) and that it's high bias. Regular cuben would just say 9K without the HB.
.18 = The thickness of the mylar layers, .18 is the same stuff used in 1.5oz (CT5K.18) and 1.2oz (CT3.5K.18).
Your cuben is extremely bomber (and heavy) stuff. 1.5oz cuben is considered bomber (ie. rodents can barely chew thru it) and your cuben has way more spectra than that. It's almost as heavy as 210D dyneema grid nylon. This cuben sounds decent for a pack, but it's overkill for most other stuff. People typically use CT1K.08 or CT2K.08 for stuff like tarps.
Regarding the shoulder straps, I wouldn't try this unless I also had a good ridgid frame. With a frameless pack I think it would sag down until the shoulder straps do contact your shoulders, so essentially you'd be making a pack with too long of a torso. I know what you mean about using the hipbelt to get the load off your shoulders, but I don't think I'd want to commit to always having enough rigidity to keep it like this. If find my frameless packs sag down until the shoulder straps do wrap around my shoulders.Nov 4, 2010 at 4:02 pm #1661170
Thanks, but no. I found that one ok–but somewhere (I thought it was here) I read what the viarous numbers meant, in terms of film thickness, fiber size, etc. It won't make a difference as to whether or not I use the stuff I have, but I'm curious about the effects of those variables on the feel and look of the Cuben. My pack is for sure going to look a lot more white and less translucent than the stuffsacks and dog dishes I made out of the stuff from Quest.Nov 4, 2010 at 4:13 pm #1661181
Yeah, I know it's probably overkill, but when I'm on the AT, I tend to fall down a lot, so I figure I'd better play it safe. And my tarp will be from the usual much lighter stuff.
As for the straps, I know I had the torso collapse thing going with a frameless Golite pack some years ago. But the corrugated plastic with thin metal rods that's in my old Infinity worked really well, and I would make the framesheet long enough to include the strap attachment point. On the Infinity, the load lifters are attached just above the framesheet, which limits their effectiveness. I've stuck that framesheet into the hydration pocket of my Mariposa, and I really like the way it carries now, and I can keep the strap weight mostly off my shoulders. From a mechanical standpoint, I can't see a difference between normal straps w/ load lifters and the high straps I'm proposing–but then, I'm not an engineer…Nov 4, 2010 at 4:19 pm #1661183
Has anyone seen any specs for this product code yet? I've emailed Jon at Cubic Tech about it but he hasn't responded to me yet.Nov 4, 2010 at 4:28 pm #1661188
What specs are you looking for? It weighs 1.2oz and the rest of the specs are in the name. It uses the heavier .18 mylar layers and it still has a lot of spectra (3.5K) so it would be great for stuff like tent floors, groundsheets, rain pants etc.Nov 4, 2010 at 4:30 pm #1661190
Or do we just assume that it has the same warp break strength as CT3.5K.08?Nov 4, 2010 at 6:17 pm #1661237
Brian SenezBPL Member
How do you calculate the weights of the various cuben products? I know there is .33, .48, .74, 1.2, and 1.5oz I'm having a little trouble matching those up with the chart.Nov 4, 2010 at 6:30 pm #1661243
Jim ColtenBPL Member
Cuben's heritage is in sail making, a result of which is that when they speak of a yard they mean a sailmakers yard … 28.5"x36"
I rely on GOG (Good Old Google) to convert between various units … feed it Grams/meter^2 in ounces/yd^2 and it'll respond "1 grams / (meter^2) = 0.0294935247 ounces / (yard^2)"Nov 4, 2010 at 8:44 pm #1661279Nov 4, 2010 at 8:57 pm #1661282
Bill FornshellBPL Member
@bfornshellLocale: Southern Texas
A long, long time ago when I first starting using Cuben Fiber I would order the lightest they had and when I received it, cut a 36 inch square piece. Then I would weigh it and figure the weight per square yard.
Anytime I bought a different product code I would do the same thing. Now I know the sq yard weight of what I use.
I would recommend you do the same.
When working with Cuben Fiber their are no real short cuts to what you try yourself.Nov 4, 2010 at 9:37 pm #1661295
"How do you calculate the weights of the various cuben products? I know there is .33, .48, .74, 1.2, and 1.5oz I'm having a little trouble matching those up with the chart."
To match those weights up to Cubic Tech's charts you need to convert it from oz/yd2 to grams/m2 which Cubic Tech uses. So first you take the weight of cuben (ie 0.74) and multiple that by 28.4 to convert it to grams. So 0.74oz/y2 x 28.4 equals 21.0 grams/yd2. Now we need to convert those yards to meters. A meter is 39.4", so a meter squared is 1.2x bigger than a yard squared. So we take our 21 grams times 1.2 and we get 25.2 grams/meter2.
In short it's: oz/yd2 * 28.4 * 1.2 = g/m2
Insert any weight (0.33, 0.48 etc) in for the oz/yd2 and you'll get the answer in g/m2 which will then match up fairly closely with the numbers in Cubic Techs chart.
The chart posted above makes this easy for you, but some weights of cuben are not in the chart. For example 1.5oz cuben is CT5K.18
The new 1.2oz cuben is CT3.5K.18, so you can see that the heaver .18 mylar layer doesn't add a lot of weight because CT3.5K.08 (same thing but with thinner mylar) is still 1.05oz. So it adds about .15oz to get the thicker mylar.Nov 4, 2010 at 10:09 pm #1661303
How sure are we as a community of the weights of these unpublished part numbers such as CT3.5K.18 and CT5K.18? I wish CT would just keep their data sheet up to date! Note there is a discrepancy between 3.5K.08 to 3.5K.18 (adds .15 oz/yd for the thicker mylar) versus 5K.08 to 5K.18 (adds .28 oz/yd for the thicker mylar). This tells me that the 1.2 and 1.5 oz/yd are rounded or estimates and thus not to be trusted.
EDIT: It seems I was right about 1.2 and 1.5 not being accurate. From below we see that the real weights are 1.26 and 1.43! There is much less difference between CT3.5K.18 and CT5K.18 than previously thought.Nov 4, 2010 at 10:25 pm #1661312
"How sure are we as a community of the weights of these unpublished part numbers such as CT3.5K.18 and CT5K.18? I wish CT would just keep their data sheet up to date!"
Cubic Tech is keeping their data sheets up to date. It's just that the ones people are posting here on BPL aren't the most recent ones. Somewhat recently (ie. August) Cubic Tech began requiring non-disclosure agreements before they'd send out their specs sheets, so less people have the most recent ones. If you want the latest specs you can email CT and ask, and once you sign a non-disclosure agreement they will email them to you. Kinda lame IMO, but that's the way it goes. I do have a spec sheet with 1.5oz cuben on it from July:
As per this sheet, 1.5oz cuben actually weighs 1.42oz/yd2 if Cubic Techs specs are accurate.
CT5K.08 works out to 1.22oz/yd2, so the heavier mylar seems to add about 0.2oz/yd2. I'd love to see them use this heavy mylar with less spectra (ie. 1K or 2K) to create a more abrasion resistant variant around 0.7-0.95oz/yd2. This could be a great tent floor material. 1.5oz cuben is bomber stuff, but it's heavier than necessary since you really don't need 5K worth of spectra. I suspect CT is working towards this. This spring you could only get CT9K with the .18 mylar, then they came out with CT5K.18 in early summer and now CT3.5K.18 a few months ago. I'm sure they would make CT2K.18 if a manufacturer asked and was willing to buy 99 yards. Maybe Zpacks or HMG could do this.Nov 4, 2010 at 10:37 pm #1661320Nov 5, 2010 at 11:54 am #1661469
Nice work on the chart!
Regarding the strength of CT3.5K.18, it seems quite likely that the strength specs are the same as CT3.5K.08 because the specs for CT5K are the same with either the .08 and .18 mylar.
Regarding a lighter variant using .18 mylar, my understanding is that Cubic Tech has signed a few exclusive tent contacts with Terra Nova and Brooks Range. The MYOG'er can make one, but Cubic Tech won't sell large quantities to other companies for the purpose of tents. The point here is that the MYOG market is likely too small for Cubic Tech to be concerned with developing variants for….and this new variant would perhaps just steal sales from existing variants (CT3.5K.18) rather than actually increase overall sales, so Cubic Techs motivation to offer even better products may be low. I'd love to see it and maybe they will come out with it, but it might take one of those two companies asking for it to happen. If it does happen, I think we'll see CT2K.18 next and then maybe they'll keep going and do CT1K.18.
You might be wondering if these exclusive deals are true, then how can companies like Zpacks, Lightheart, HMG and MLD sell their wares? Zpacks and MLD technically only make cuben tarps. Neither sells a true tent with a floor. HMG might have a deal with Cubic Tech..or maybe they're allowed to do their thing because Cubic Tech considers the Echo a tarp since it doesn't use tent poles and can be set up as a tarp. Lightheart seems to clearly be making a cuben tent, so I suspect that the volumes of cuben they have ordered so far and simply low enough that Cubic Tech hasn't noticed. Perhaps they have a deal, or perhaps they'll run into trouble down the road once they really get production fired up and start needing larger quantities of cuben.
It seems to me that a tent floor or groundsheet doesn't need a huge amount of outright strength, it more needs reasonable strength combined with good abrasion resistance. So something like CT1K.18 @ ~0.71oz/yd could be perfect. CT0.6K is barely lighter (0.48oz vs. 0.51oz) so it doesn't seem worth it and CT0.3K.18 might work but I don't think any one is going to want to commit to buying 99 meters of it to test it out. CT1K.18 or CT2K.18 sound like the sweet spot to me for a floor.Nov 5, 2010 at 1:17 pm #1661491
I've also considered going with CT0.0K.5 for a tent floor which it turns out is insanely cheap! I kid a little since we're geeking out on CT products but honestly I think 100 gauge mylar may make a fantastic tent floor and the price is right.
Has anyone tried this yet or ruled it out for a reason I have not yet thought of?Nov 5, 2010 at 2:13 pm #1661513
I wound up fooling around with the product codes and weights a little more and have managed to establish that the thickness of the mylar is in mils (thousandths of an inch) per layer. For instance two 0.08 layers of boPET (Mylar) weigh 0.17 oz/yd² at an assumed density of 1.39 g/cc. This immediately allows us to deconstruct the products in a very useful and interesting manner.
Thus we can see at a glance that CT1K.18 would weigh 0.72 oz/yd² and my dream material, CT0.3K.18, would weigh 0.55 oz/yd². Also this seems to indicate that the true weight of CT3.5K.18 would actually be 1.25 oz/yd² rather than the oft reported 1.20 oz/yd².
EDIT: Updated to reflect the true weight of CT3.5K.18 reported by Joshua below.Nov 5, 2010 at 2:22 pm #1661515
Joshua GrayBPL Member
Hey everyone, i think i posted these numbers in a different thread a while ago, but here are the numbers for warp break and load for the CT3.5K.08 and CT3.5K.18.Nov 5, 2010 at 4:20 pm #1661558
Nice work on the chart. One thing that would be nice to know is what is a 'K' worth of spectra? Ie. maybe it's 1000 strands per yard? And is that in each direction? Or 500 each way for 1000 strands total? Or maybe there is the same number of strands in all weights of cuben and K refers to the thickness of the spectra (I suspect this is wrong). Or maybe it's the total weight of spectra and both the number of strands and the thickness varies?
Also, it has always seemed odd to me is the tiny weight difference between CT0.6K and CT1K. How could 0.6K worth of spectra weigh 0.30oz when 1K weighs just 0.34oz. You'd think 1K would be around 2/3rds heavier than 0.6K. Maybe it is and the specs are off?Nov 6, 2010 at 11:10 am #1661692
Apparently one of our beloved cottage gear manufacturers may order a roll of CT1K.18 early next year. I call dibs on the fist 6 yards!Nov 6, 2010 at 12:10 pm #1661698
Nice…hopefully it happens.Nov 6, 2010 at 7:19 pm #1661779
Dustin ShortBPL Member
Curious. I'm thinking that maybe the thickness of mylar is measured as the layer above the spectra threads. Since the threads have a thickness, extra mylar is used to adhere to the spectra layer. This could be a fairly large amount of mylar, so adding extra spectra only bumps up the weight a little. Complete conjecture on my part of course.
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