waterproof backpack fabric

[Jennifer Kilpatrick]

Hello, I'm about to start a project to create a waterproof backpack with removable frame. The main compartment, backpack lid and the front pocket will be waterproof. I've sketched most of the backpack and have an idea of how it will look like, and thanks to many previous projects already done and displayed here I have an idea on how to make it. I want this pack to be completely water proof and lightweight so I don't have to use stuff sacks or pack liners, my question now is, what fabric/s should I use? I've thought about using cuben fiber but it's expensive, hard to work with and it's subject to abrasion damage. I've sewed clothes before but never made a backpack, so any advice would be awesome.

[David Drake]

X-Pac would be a good choice. Rockywoods and DIY Gear Supply both sell it.

[David Ure]

FWIW, I just used an HMG Porter on the West COast Trail and the fabric proved both waterproof and amazingly abrasion resistant and I bushwacked with it and scraped it over logs.

[Jerry Adams]

I just use silnylon but most people think it's not strong enough. Works for me but I don't do a lot of bushwacking or anything.

If you use silnylon, most of it is not waterproof. I coat the inside with mineral spirits/silicone which works, but maybe better to use the "Shield" silnylon from thru-hiker.com which is waterproof.

[Terry Trimble]

It all depends on how waterproof you want the pack is waterproof as the Arc'teryx Arrakis waterproof pack for example. Arc'teryx uses heat sealable fabric all the seams are taped or sonic welded. You can buy heat sealable fabric from seattle fabrics.
For our use Xpac is the best because of the PET film laminated to the pack fabric then make all seams flat seams and then use Melco or Bemis iron on seam sealing tape on all seams on the inside the pack so they don't leak.
Terry

Seattle fabrics:
http://seattlefabrics.com/nylons.html#heat%20sealable%20packcloth

http://seattlefabrics.com/Seam%20Sealers.html

Xpac is from Rocky woods fabric:

http://www.rockywoods.com/Fabrics-Kits/All-Ripstop-Nylon-Fabrics?range=21%2C40%2C43

http://www.rockywoods.com/Hardware-Zippers/Seam-Sealers-Seam-Tapes

[Jennifer Kilpatrick]

I don't do bushwhacking and I take care of my stuff, so I don't need the fabric to be super strong. I do need the fabric to remain waterproof for the life of the backpack and not fail from basic use such as setting my pack down on grass, rocks or anywhere on the trail. I will be using a tougher fabric on the bottom of the pack and a lighter on the sides ofc =). There are many types of silnylon and x-pac fabric, do you guys have suggestions of which in specific should I use for the lightest weight possible?

[David Drake]

You'll prob. find once you calculate the area of your pattern pieces and the weight of the fabrics that the weight savings between the various x-pacs and silnylons is only a few ounces–maybe not that big a deal, relative to the weight of the frame system and features you're planning.

I made a 30 liter frameless pack with vx-21 bottom, front and back and 1.9 oz silnylon for the sides–I suspect combining silnylon with x-pac means seam tape won't work (won't stick to silnylon). Total surface area is ~0.8 square yards, so differences between x-pac (vx-21 6 oz/sy) vs. 2.92/1.43 oz Cuben vs. 1.9 oz silnylon isn't great, in terms of actual ounces.

[Jerry Adams]

I've done 50 or 100 nights with silnylon.

Before I put silicone/mineral spirits over entire inside surface, when I had an insulated garment touching the fabric, and it rained, water leaked through fabric and got insulated garment wet.

I noticed on recent trip it leaked a little at one seam – but that was a place where water collects – need to re-seal it.

The "Sheild" silnylon from thru-hiker.com is waterproof without any treatment, although you would need to seal seams.

[Jennifer Kilpatrick]

I'm making the frame out of hollow aluminum tube and a foam pad, the tube and pad will be removable, the hipbelt as well to save weight depending on what I'm taking inside. I want to save weight on the fabric now rather than be sorry I didn't later.

I could use the coated silnylon from thru-hiker on the sides and 70D at the bottom then sealing all the seams with silnet, or using the heat sealed fabric Terry suggested and going 30D on the sides and 70D at the bottom.

The maximum weight I would ever carry on the pack will be around 40lbs, but most of the time with maximum load of food water and fuel will be around 15-30lbs. The pack only needs to be waterproof against rain, storm, snow etc… no full submersion, I have yet to drop a pack in any body of water.

The X-Pac seems very tough but I don't know if being 5 times as heavy as silnylon for being extra strong is worth it, kindy like taking an extra flashlight or something that is "just in case". I'm no expert in such fabrics though, so I could be way off.

Any thoughts?

[Nancy Twilley]

I think at this point it's personal preference — I wouldn't personally use 70D for the stronger sections of the pack, I'd use something tougher, like Xpac. But plenty of people DO use 70D fabrics or lighter for packs, and are quite happy to do so.

Hike your own hike! If that fabric combo makes you happy, then roll with it.

[Jerry Adams]

Like David said, you only save a few ounces using silnylon rather than X-Pac, but

Silnylon works and is a little lighter so may as well use it

If you did all X-Pac, you wouldn't need a reinforcing piece at the bottom and avoid that seam which can leak.

Most people seem to be using X-Pac or similar and seem to be happy

Currently I use 200D fabric on the bottom for reinforcement, but maybe next time I'll just do the whole pack out of silnylon. Even if there was an abrasion hole, maybe rain wouldn't find it's way in. On top is where it's more important.

[Sam Farrington]

Am in the same situation, and just ordered some 200 denier military spec material that looks like it may work. If it lives up to expectations, will post on this thread.

[Roger Caffin]

I make my packs with X-Pac, and I tape-seal the seams. The pack is waterproof: I don't use a pack cover.

> I don't know if being 5 times as heavy as silnylon for being extra strong is worth it,
There's a wide range of X-Pac weights available, from little more than silnylon to 1000 denier Cordura. The toughness matches the weight.

Cheers

[Jennifer Kilpatrick]

What's a good lightweight X-Pac that I can use on the pack? All the ones I've seen are heavy.

And what about X-Pac makes it stronger?

I've read online that silnylon is a slippery fabric, how will that effect the backpack?

[Jerry Adams]

silnylon slipperiness – If you sew together two long pieces, like for a tent, as you're sewing, the two pieces can slip relative to each other so by the end of the seam, they're not lined up. You have to worry about this a little for a pack. Practice sewing some pieces to see how to control it.

[David Drake]

Hi Jennifer,
DIY Gear Supply lists tx-07 as the lightest x-pac they carry, but doesn't list actual weight. The face fabric is 70D nylon–I'd guess maybe 2.5-3 oz/sy? I assume vx-21 is the heaviest (the vx-21 I've used weighs out a bit lighter than the 6 oz/sy Rockywoods lists). You could email DIY and ask for weights–the owner sometimes posts here as well.

Something to think about re: different fabrics for sides/bottom/back/front. Using one fabric for the whole pack means you could reduce the number of seams, which means fewer potential points of failure if waterproofness/durability is a priority. Could simplify construction as well. I'm considering this as I design my next pack.

Edit: Oops. Just saw Jerry made the same point re: number of seams up thread. Do you have samples of any of these fabrics? If you send me a PM, I could mail you a scrap of vx-21 as well as 30D and 70D silnylon.

Second edit: I meant tx-07 as "lightest" above.

[Michael Duke]

I have used vx-21, tx-07, vx07, and DX40, and I have handled the rest that DP carried last year. TX07 is a really nice fabric. It is a 70 denier face fabric with polyester reinforcement and a PET backing. I like it a lot. If you would like to see how it looks, I posted a thread yesterday of a few packs, and the TX07 is the blue fabric.

[Ryan Smith]

Some folks have used TX07 as a pack fabric and had great results as far as abrasion and toughness. It is 2.9oz/yd from memory. Based on your requirements above, I would use this.

Ryan

[Jennifer Kilpatrick]

The TX07 looks very good and it's light enough, I could make my whole pack with it, would save money from buying multiple fabrics. I'm still thinking of making the pack out of Cuben fiber too, I just saw at quest outfitters they have "cuben tape", no sewing and 100% waterproof, will make the job much easier and faster, wonder if that tape works on other fabrics too, then maybe I could use cuben on top and TX07 at the bottom. Michael, since you made packs with both fabrics, what do you think?

[Michael Duke]

It depends on your pack design. I would be skeptical of bonding if you have webbing in the seams. If it's only cuben and nothing sandwiched in the seam, it could work. I always sew though and do not have experience bonding.

Personally, on the bottom, I would use a thicker material than tx07. The bottom is a small part that takes a lot of abuse. Weight savings here are minimal, as it is such a small area. Two of those packs have DX 40 bottoms, which is really thick, and the other has a VX21 bottom. The frameless cuben one uses 2.4 ounce cuben, vx21, and dyneema grid and still comes in under 9 ounces, so the weight penalty for more durable materials is pretty minimal.

[Brendan Swihart]

Something to consider re pack fabric weights: Most UL style packs only use around a square yard of fabric, so the weight savings of using something like VX21 vs cuben is only a few ounces and the improvement in durability is huge. Where you can really save weight is on webbing, buckles, 3d mesh, etc. I've made packs out of everything from cuben to DX40 and have decided that the lighter stuff isn't really worth the minimal weight savings (after a big hole in a cuben pack from minimal abrasion the first day I used it).

On the other hand, once you make your first pack you'll be hooked and be immediately planning your next one so maybe durability isn't a big deal at this point ;)

[Steve C]

You mentioned waterproofness as a goal and there has been some talk about taping seams. The WX and TX line of fabrics have the PET as one of the faces. VX has 50d for one of the faces and the PET sandwiched so I can see how you would tape it. When using the TX line how does the PET face wear as a pack exterior? (Assuming you have taped interior seams) Or do you have to apply a seam sealer on the seams from the outside and have the PET face on the inside of the pack?
As an aside…I find the "lt gray" TX07 to be more like off white.

-Steve

[Brendan Swihart]

I've done some tape testing on the mentioned fabrics. The McNett iron on tape adheres very well to the VX taffeta back and fairly well to the TX/WX back. I've also made tape using 3M 9485 and a lightweight urethane backed taffeta or cuben. Works great with all of the above fabrics. None of the tapes adhere very well to the face fabric, probably due to the DWR.

[Roger Caffin]

3M9485 tape onto the coated face of 70 gsm PU-coated nylon fabric, onto the tricot knit face of the X-Pac on the inside. Rub down hard and leave for a day.

Have to avoid friction from gear which can peel up the end of the fabric 'tape', so some thought over the layout of the taping is good. Problem is mainly at the top of the bag: ends at the bottom just get 'sat on'.

No, 3M9485 will not adhere very well to the DWR-coated face fabric on X-Pac, quite right. Not much else will either (PU, silicone …)

Cheers

[Steve C]

Brendan,
Not sure I am following you, did you use two sided tape and cover the seam then cover the tape with a strip of fabric?

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