Fiberglass cloth, silicone, and questions in relation to packs

[Justin W]

I’ve been wondering why fiberglass cloth isn’t used for backpacks? If you compare the specific strengths (tensile strength in comparison to the material’s density) of nylon 6 vs E grade fiberglass fibers, fiberglass has two and half times higher specific strength (if you use S grade fiberglass cloth, it will be 3.4x higher specific strength).  If you are curious, E glass fiber glass’s ultimate tensile strength is 5.6x higher that of nylon 6’s, but again, when you factor in density and that fiberlgass is about 2.24x more dense than nylon, it does lower the overall strength to weigh ratio in comparison.

Besides its significantly higher specific strength as compared to nylon 6, it has other attractive properties. It doesn’t absorb moisture, it is not affected by UV at all, very high microbe resistance, it is inexpensive (especially when you buy in bulk–typically at least 16 yards), it can handle very high heat with no issues (unlike nylon), and it’s more stiff than nylon (which in a pack I think is a good trait because it will carry weight better).

The downsides are that the fibers are potentially irritating to the skin* with less flex durability than nylon.  * To me, the former is a non issue because if you use fiberglass cloth, you have to encapsulate it within a bonding matrix of some kind, which for my purposes, I would use thinned silicone caulk (because of accessibility, expense, relative ease, and you can bond to other silicone coated fabrics).  If there is a thick enough coating of silicone over the fibers, there won’t be any chance for the fibers to come out of their yarn and weave.

As to the second part of this, I think it is less important for a piece of gear like a backpack than it is for say clothes, tarps, tents, and the like, where the latter often get folded over, twisted, etc. repeatedly. In all reality, a pack only has to flex and fold a little here and there.  Comparatively, it is a more static and homogeneous shape/structure/function.

I guess the other downside is that you would have to make the fabric yourself (treat the fiberglass cloth with silicone and/or silicone bond it to other silicone coated fabrics), but this is not a barrier to me or most DIY/MYOG type folks.

More specifically, why couldn’t you say, take a 2.1 or 3.7 oz/yd2 fiberglass cloth and silicone bond it to silpoly (for greater waterproofness and better sewing), and have the light weight silpoly fabric on the inside and the siliconized fiberglass on the outside?  Silicone is considered to have significantly better UV resistance than nylon and even more than polyester, and as mentioned the fiberglass cloth is unaffected by UV and so, the material would last as long as the silicone does.

Honestly curious why something like hasn’t been done by people before?   Am I missing something major?

Another cool thing you could do with fiberglass cloth, is if you wanted a very stiff framed, high load backpack, you take a piece of thin’ish plywood and bond fiberglass to it with high strength epoxy and for the rest of the bag that is meant to be flexible, you do the above of siliconzing it and bonding it to a silpoly. If constructed well, theoretically such a pack could carry very heavy loads well (good for hunters or the like).

Seems like a decent and more low cost alternative to UHMWPE fabrics.  Besides the expense of these fabrics, bonding to them is very difficult unless they are specially altered by cold plasma treatments or the like. Not easy to do for the average DIY’er.  Meanwhile, they need to have some kind of film or bonding agent otherwise the fibers can come apart within the weave (and for waterproofness).  If inexpensive and bondable/already treated UHWMPE fabrics ever become a thing, then yeah, this would be the ultimate pack material, but meanwhile, if I’m not missing anything, it seems like fiberglass cloth/silicone/silpoly composite fabric would be an improvement over other inexpensive options as to strength per weight and especially long term durability (particularly due to very high UV and microbe resistance).

[Justin W]

You can buy pre siliconized fiberglass cloth, but from what I’ve seen, you can only buy heavy/thick versions of it, often in satin weave (plain weave would be better imo).  Typically it is around 14 oz/yd2 or more.

[Jerry Adams]

interesting ideas

maybe lightweight fiberglass fabric for ultralight backpacking is too niche

if it could be developed for sails on sail boats, that would be a bigger market with similar requirements. I wonder if they’ve ever done that?

and sails are better if they’re not stretchy.  I think tents are also better if not stretchy.  Fiberglass must be less stretchy.  Maybe doesn’t matter for packs to be stretchy, but like you said, I think pack fabric is better if stiff.  Maybe stretchy and stiff are the same.

[Justin W]

Fiberglass fibers do have some stretch to them (once near their breaking point) as compared to say carbon fibers, which actually makes them tougher/more durable in a way, because if there is a lot of tension put on them, they tend to elongate before completely breaking, whereas carbon fiber can catastrophically burst/splinter once it nears the upper part of force it can handle (in that sense, CF is more brittle and part of why it doesn’t handle impacts very well as compared to things like fiberglass, kevlar, etc).

But it doesn’t have regular stretch like say nylon does.  Nylon is somewhat hydrophilic (4% moisture regain) and also inherently stretchy, but it stretches even more when it is wet.  Fiberglass doesn’t absorb and isn’t affected by water in that way. (Different than the issue of say fiberglass insulation batts that can hold water in between the fibers and eventually allow mold etc to grow in between the fibers.)

I’m not sure if sails were ever made with a siliconized fiberglass cloth.  I think people are so used to thinking of fiberglass as reinforcement for epoxy and polyester resins, that maybe they just have overlooked other uses?

But I could be missing something. This is why I posted, to see if anyone knew of anything I might be missing. I’ve worked with fiberglass cloth before, but in the more normal ways (with epoxy etc).

Here is a link that goes over the properties of fiberglass: From said link:
http://www.lewcospecialtyproducts.com/products/reinforcement-coating-laminating-fabrics/properties-of-fiberglass-fabrics/

“CHEMICAL RESISTANCE

Fiberglass textile fabrics will not rot, mildew or deteriorate. They resist most acids with the exceptions of hydrofluoric acid and phosphoric acid.

DIMENSIONAL STABILITY

Fiberglass fabrics will not stretch or shrink. Nominal elongation break is 3-4 percent. The average linear thermal expansion coefficient of “E” glass is 5.4 by 10.6 cm/cm/°C.

GOOD THERMAL PROPERTIES

Fiberglass fabrics have a low coefficient of thermal expansion and relatively high thermal conductivity. Glass fabrics will dissipate heat more rapidly than asbestos or organic fibers.

HIGH TENSILE STRENGTH

Fiberglass yarn has a high strength-to-weight ratio. Fiberglass yarn is twice as strong as steel wire.

HIGH THERMAL ENDURANCE

Fiberglass cannot burn and is basically unaffected by curing temperatures used industrial processing. Fiberglass will retain approximately 50 percent of its strength at 700°F and as much as 25 percent at 1000°F.

LOW MOISTURE ABSORPTION

Fiberglass yarn has extremely low moisture absorption.”

 

 

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