Material Perception

Paul,

" Corduras are the worst in that regard, they never have a thick enough coating to deal with the rough texture of the fabric, so pinholes are normal right from the start and get worse quickly".

+1 for that statement.

While I used 500D Cordura fabric for abrasion resistance on the bottom of my pack I found out recently that despite the coating it is not at all waterproof IME.

A fellow hiker had refilled his hydration reservoir before turning in for the night. Unfortunately he set his pack down on the reservoir's bite valve. It emptied out the H2O onto the floor of the hostel where we were staying that night. My pack was soaked from the bottom up. It's just one more reason to use a pack liner. ;-)

Party On,

Newton

Do the heavier weight fabrics have bigger threads, which means it's more difficult to get a good coating? There's a bigger gap between threads that has to be bridged by the coating, which makes it fail?

Jerry,

Paul M. said;

"Corduras are the worst in that regard, they never have a thick enough coating to deal with the rough texture of the fabric, so pinholes are normal right from the start and get worse quickly".

This hypothesis seems quite feasible to me. Maybe if Roger Caffin is listening he can chime in on this conversation.

Based solely on my experience as noted earlier I'd have to say that IMHO the coated Cordura is at best only water resistant and not waterproof. YMMV

Extreme X-pac VX51 has a 500 x 1000 denier Cordura Nylon layer plus the 0.25 mil PET film layer and a DWR. The fabric weight is 10.4 ounces per square yard for the VX51. This could be the ultimate abrasion resistant water proof pack bottom material with the exception of the needle holes. ;-?

I do wonder how easy it would be to work with due to the probable stiffness and thickness of the fabric. I think I have some swatches of this fabric. I'll have to check on the pliability of it.

Party on,

Newton

"While I used 500D Cordura fabric for abrasion resistance on the bottom of my pack I found out recently that despite the coating it is not at all waterproof IME."

Indeed, this has been my experience as well. 210d isn't much better.

Using the same abrasion test, the VX51 did 600 cycles compared the the much lighter VX42 with 570 cycles. I realize this is in a lab and not the real world but its still very interesting that the lighter smoother face material did almost as good. Could Cordura have it wrong with their rough texture peak and valley theory for added abrasion resistance?? Who knows.. but it seems like a pack made from 100% VX42 with the packcloth face would be the ultimate bomb proof, abrasion resistant, water resistant pack.

> Do the heavier weight fabrics have bigger threads, which means it's more difficult to get
> a good coating? There's a bigger gap between threads that has to be bridged by the coating,
> which makes it fail?
You can see for yourself. Hold some light coated fabric and some heavy Cordura up to the light and compare the size of the holes between the threads. A magnifying glass may be helpful for the details.

Let me explain about this.

Once upon a time when we didn't have synthetics, we used Japara for tents and jackets. That's a cotton fabric usually made with long-staple Egyptian fibres. The world supply of Japara came from ONE loom in Bradford, UK. It was the only loom in the world which could weave the fibres at the tension required to realy get them very closely packed to block water. Yes, the loom had been modified for this. (And Asia was not making good fabrics in those days…) Then, one day, the loom finally reached its end of life: no more Japara. Panic around the gear world! Yes, well, what actually happened was that, while repairing the loom was possible, it was uneconomic. The owners could see the writing on the wall: synthetics were taking over. So they wrote the loom off.

The point of the story is that fabric has to be woven at quite high tension to get rid of those small gaps between all the threads. 'High tension' for heavy threads means a very expensive machine. Cordura is made for strength, not waterproofness. Packcloth is also made for strength, not waterproofness. So those fabrics are woven at lower tension and have big gaps between the threads.

That leads to the question of why do they bother with a coating at all? Well, in many cases the acrylic (not PU) coating is there to keep the threads in place: for structural reasons, and to stop massive fraying when the fabric is cut. It is NOT there to make the fabric waterproof. If you want to cut UNcoated Cordura or packcloth, you really need to do it with a hot knife – or face considerable wastage at the edges.

OK, back to the problem. Trying to combine serious Cordura and 'waterproof' is not easy, and most Cordura fabrics don't really offer that. So hen I use a Cordura fabric on the bottom of a pack, it goes over the lighter waterproof fabric. It does not try to replace it.

Cheers

Roger (Caffin) mentioned defunct Japara cotton, but Ventile (cotton) is still made, and sounds very similar: used double it is viewed as waterproof (rainproof?). Jackets are still made from it: but expensive to buy ready made.

It seemed a forgotten technology by the time Goretex appeared.

That makes sense, Roger

Then there's really no reason for Cordura in lightweight gear

Unless you want to slide it around on rock or maybe bushwacking in thorns

Nice Thread, Lawson. Very helpful for MYOG.

I found my swatch of VX51 Graphite color X-pac fabric.

In handling it in comparison to swatches of VX21 and VX42 here are my subjective trying to be objective observations. ;-)

I layered a swatch of "21" and "42" together and flexed them a.k.a. bent back and forth. I then flexed the "51" by itself. What I found was that the 51 seemed noticeably stiffer than the layered combo of 21 & 42.

Caveat: Keep in mind that the combo was not bonded or sewn together in this rather quick test.

The thickness of the combination of the 21 and 42 seemed to be still thinner by perception and "feel" than the 51.

From what I gathered from my observations is that while the 51 is definitely thicker and heavier with patience and care it does seem to be flexible enough to be used on a pack bottom sewn at home on a MYOG home style machine. YMMV

Keep in mind that not all machines are made equal and some hand/manual advancing of the machine may be needed at times.

I would suggest limiting the difficulty by sewing up the corners of the bottom as if you were constructing a bathtub style floor for a tent. Then sew this assembly to the lower end of the pack body by stitching around the circumference of the pack body and pack bottom. Follow up on this with a top stitch of the seam allowances and the seam thicknesses should be manageable.

Party On,

Newton