Aqualab - Caving Overalls Fabrics

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Research Topic: Caving Overalls Fabrics

By Ian Mander, 26 February 2018, updated 14 March 2018 (pics added). This topic requested by friends who are thinking of having their own caving overalls made.

Question: What's the best fabric for making caving overalls that doesn't cost ridiculous amounts? (Shipping on Cordura from the USA is horrendous.)

Answer: At time of writing, 1000D Kodra nylon. It's rugged (testing yet to be done) without being too inflexible, has a heavy PU backing and a water repellent coating, and is available in Auckland for a much more reasonable price than importing stuff. For something even less expensive (and more colourful than just black the 1000D is available in) there are a couple of other options but some more testing will need to be done to figure out the most suitable.

Background

Overalls are commonly available from safety equipment shops for around $90, or second hand for anything from $10 up. They are typically made from polycotton (65% polyester, 35% cotton) or cotton drill (100% cotton), both of which soak up water like crazy. That drawback isn't good for caving.

How much water? I weighed a newish pair of size 8 polycotton overalls at 867 g when dry. Light drips of water beaded on the surface momentarily but the fabric readily absorbed water. Soaking wet straight out of the water the overalls were about 2000 g, reducing to 1750 g when the dripping had significantly slowed (a quite arbitrary measuring point), meaning almost 0.9 kg to over 1.1 kg of water.

Cotton drill overalls are even worse. An old pair weighed 896 g dry. Water splashed on it was soaked up immediately and it ended up about 2800 g soaking wet, dropping to 2150 g when the dripping had slowed. That's 1.25 kg to more than 1.9 kg of water.

My present nylon overalls, homemade just over three years ago (and quite heavy use for the first two of those), now have quite well worn nylon. They are double layer in places, have heavy duty stitching and zip, and a Velcro flap over the zip. The backing has worn off the inside of much of the right side of the overalls. (I must go through most squeezes on my right side.) The overalls weigh 966 g when dry and increase to just over 1.6 kg when soaking wet, quickly reducing to a bit over 1.5 kg, meaning 0.57 kg to 0.65 kg of water. That's only 58% of the water absorbed by the almost new polycotton overalls, and they dry more quickly than polycotton. It's a big improvement, but it's still more water than really wanted.

Fabric	Overalls Dry Weight	Dripping Mostly Stopped	Soaking Wet (eg, straight out of a pool)	Proportion of Original Weight	Water Weight
Polycotton (newish)	867 g	1750 g	2000 g	202% to 231%	883 g to 1133 g
Cotton Drill (old)	896 g	2150 g	2800 g	240% to 313%	1254 g to 1904 g
Nylon (homemade overalls, 3 years old)	966 g	1540 g	1620 g	159% to 168%	574 g to 654 g

Large amounts of extra water can be a big problem.

The water weighs down a caver. This in itself is not necessarily a major problem because for polycotton overalls it would be less than 1 kg most of the time (unless recently refreshed by crawling through a puddle or jumping in a deep pool), but of course for longer trips the less weight carried the better. Putting that much weight in perspective, 1 kg is 16 of my most commonly used carabiner being carried without any thought of actually using them. (Water is thankfully cheaper than carabiners.^{[citation needed]})
Heavy wet overalls can greatly hinder movement. The wet fabric makes it harder to lift arms and legs because it grabs onto the caver's body and legs, resisting any lifting, especially if a cord or belt at the waist is not taking the weight of the lower half of the overalls. This can make flat out crawls particularly exhausting.
The water cools down the wearer because it draws heat from the caver as the caver's body tries to heat up and evaporate the water. This can take a lot of energy out of the caver leaving them much more tired at the end of a trip. Excluding water from the inside of the suit is much preferred.

Acquiring/finding/making overalls of a hard wearing fabric which does not absorb much water and drains easily (doesn't hold onto the water for a long time) should thus be a high priority for any caver who more than dabbles. Sadly, professionally made caving overalls are quite expensive and one of the most popular brands in New Zealand has a reputation for taking months to arrive after placing an order and are almost guaranteed to fit the Michelin Tyre Man better than a normal human. (Where to actually buy them from is also a question that shouldn't be a question.)

Fabric Options

I've found a couple of specialist fabric suppliers who sell fabrics that may be suitable, and made a shortlist of four fabrics. A few notes:

Denier is the thread weight used in the fabric. It's the weight of the thread in grams per 9 km of the thread; silk is 1 denier, 1 g/9000 m. Generally the bigger the number the heavier the thread and the more hard wearing the fabric is, although nylon is much harder wearing than polyester for the same denier.
The weight per area is given in grams per square metre, commonly abbreviated to gsm. It's of much more interest to someone using a fabric, not to the shop selling the stuff.
Fabrics are sold per metre length, and these options are all about 1.5 m wide.
The prices mentioned below are rounded and include GST, but the shops are wholesalers so will add GST on the total.
Shop B has a surcharge on each cut length.

As a comparison with the four fabric options I weighed an offcut of the nylon I used to make my present overalls, and an old used sample of polycotton fabric.

The nylon from my present overalls (an offcut that hasn't been caving) has an unknown white backing substance and weighs 227 gsm. Running water mostly just beads off, submerging increases weight by only about 14%, forced soaking by 38%. That's quite a bit less than the 68% increase in weight by my well-used overalls made of this fabric, and shows how much more water fabrics can absorb as they get older.

The old polycotton – a pocket removed from the overalls when it became clear they were destined to be primarily used for caving – was 309 gsm when dry but water soaked straight in and when wet was 758 gsm, 2.45 times the dry value, a 145% increase. This is the fabric I wore before changing to nylon, and when the overalls were wet I would be carrying a lot of water with me!

Fabric	Weight Thickness	Colours	Water Handling	Water Weight Gain	Cost
420D nylon with acrylic backing	171-182 gsm depending on colour backing varies a bit 0.26-0.28 mm	Many, including fluoro	Absorbs very little water. Dries extremely quickly.	43 - 56 gsm	$14.03/m (PU backer?) OR $7.75/m + $6.33 per cut length
1000D nylon with PU backing	claimed 300 gsm measured 310 gsm 0.43 mm	Black only	Water repellent coating. Water mostly beads off. Submerging absorbs some water, but more can be forced into the fabric. Dries pretty quickly.	60 - 146 gsm	$17.50/m + $6.33 per cut length
600D polyester with PU backing	202 gsm ?	9 colours	Untested. Claimed 600mm hydrostatic something.	?	$11.40/m
600D polyester with PVC backing	claimed 418 gsm measured 442 gsm 0.48 mm	8 colours	Absorbs water easily. Dries more slowly than the other options.	172 gsm	$14.70/m OR $10.32/m + $6.33 per cut length
unknown denier nylon, unknown white backing (comparison)	227 gsm 0.34 mm	navy blue	Water on surface beads off. Submerging adds a small amount of water. Forced soaking absorbs a fair bit more. Dries quickly.	32 - 86 gsm	$7/m + $4 base shipping cost (no longer available)
old polycotton (comparison)	309 gsm 0.48 mm	faded blue	Absorbs a lot of water easily.	449 gsm	~$90 and wear them for years

420D nylon with a white PU or acrylic backing

The two shops selling this say it has either a PU or acrylic backer. It looks the same product but I do not have samples of the claimed PU backed nylon so cannot make a direct comparison.

Available in a whole bunch of colours including fluoro. The different colours (shop B samples) have slightly different weights – an inconsistency which may point to lower quality. Measured weight range of 171-182 gsm, which is lighter than my present nylon. The lightest and heaviest (thinnest and thickest) do feel a little different. Acrylic backings are used to stabilise the weave, not make them waterproof, and are the cheapest and wear out quickly, so we can probably expect this fabric to soon leak like a sieve and the weave to start pulling apart. Water soaked into the fabric easily but only a very small amount of water and it dried very quickly.

Comment: This seems quite a light weight fabric and will feel a bit like you're wearing a school bag since it's got a very artificial feel to it. But it's quite cheap and colourful and will likely do an OK job (at least for a while) for less demanding cavers such as children (wearing wetsuits). Fluoro pink overalls! One of my brothers pointed out the fluoro yellow is transparent enough to show your undies underneath, and it looked waterproof enough to not breathe so it might be sweaty and uncomfortable. Meanwhile, my other brother said the backing was rough enough to take your skin off, but I pointed out the caver would probably be wearing polypropylene thermals underneath.

It's a very noisy fabric, probably a result of its plasticky feel. While sewing this stuff (especially turning them inside out repeatedly) don't be too surprised if people start closing doors and turning up the volume of the television in the next room. This is not a fabric for caving ninjas.

Shop A (claimed PU backer): $14.03/m. The price suggests a PU backer but testing would be needed.
Shop B (claimed acrylic backer): $7.75/m + $6.33 per cut length. ~$30 for 3m... er, 2.95m as it turned out; this is the first time I've ever had fabric cut short.

1000D nylon with transparent heavy PU backing

Black only, sadly. Has a water repellent protective finish and running water basically just beads off! Fast drying. Officially 300 gsm, measured 310 gsm.

Comment: This feels like a very strong/tough fabric with a good weight – a fair bit heavier than my present nylon (which seems right for the step up I personally want). It has much less of the artificial feel the 420D nylon has, but is also less flexible than it (yet still far from the stiff-as-a-board reputation the fabric of the Aspiring suits has). As it's much stiffer than my present nylon I figure it should be much less likely to wrap itself around sharp things, catch and rip. The water repellent coating probably won't last in the long term, but for now it's quite effective.

$17.50/m + $6.33 per cut length. ~$59 for 3m.

600 denier polyester with transparent PU backing

No sample. Available in 9 mostly muted colours including black but no fluoro colours. The claimed 202 gsm is a little lighter than my present nylon. Claims to have 600 mm hydrostatic something – untested. Will noticeably fade from UV after a year or two outdoors – shouldn't be a major problem underground.

Comment: It felt quite thin and light weight, which makes me wonder how well it would last, but for less demanding cavers it would probably be fine. Smoother more natural feel than the nylon 420D and probably a better option in the long term because of its much better backing, but it might absorb an undesirable amount of water – that needs to be tested.

Shop A: $11.40/m. ~$34 for 3m.

600 denier polyester with a black PVC backing

Available from Shop A in 8 mostly muted colours including black, no fluoro, and from Shop B possibly only in black. It's similar to the other polyester above but the PVC backing makes it heavy and thick. Claimed 418 gsm, measured 442 gsm. Water soaks straight into the fabric and took a while to dry. Will noticeably fade from UV after a year or two outdoors – shouldn't be a major problem underground.

Comment: Being so heavy and thick you'd have to be pretty keen to want to make a whole suit from it, but you'd certainly feel like you were equipped to face anything. I've been given a sample piece 152cm x 98 cm that the guy said he wouldn't be able to sell – very generous of him, since he could have cut it up for samples. The surface has a nice soft feel in the length direction, a bit rougher across. With the PVC making it waterproof it might be best used as a waterproof layer on the backside and knees of one of the two cheap fabrics, especially if it had a spray-on silicone waterproofing treatment.

Shop A: $14.70/m (8 colours).
Shop B: $10.32/m + $6.33 per cut length (possibly black only). ~$37 for 3m.

Other Notes

All the above fabrics are easy to flex but don't drape (hang) like my present nylon, so they don't behave like "normal fabric" like polycotton overalls do. I suspect the higher denier fabrics absorb more water than the 420D nylon because of their more natural feel. It's probably a direct consequence of not feeling like plastic sandpaper.

Even if the three fabrics with PU and PVC backings absorb water, the backing should greatly help keep water on the outside, especially so with the PVC. The greater stiffness of the fabrics will also help prevent the fabrics gripping onto the body and legs.

I couldn't tear any of the fabrics with my fingers but could distort the edge of the 420D nylon, pulling the fibres apart but not breaking them. It's the only one I could make any visible impact on, and will be a direct result of the lower quality backing used. It's probably a sign of what's to come. When the acrylic backing is gone (which might takes years of intermittent caving), the nylon fibres will have little to hold them together so will start to fall apart with even moderate treatment. At the least, with larger cavers I expect the stitching holes will open up.

Conclusion

Each of the four options has some attractive features and some drawbacks.

420D nylon with white acrylic backing. This is the cheapest, but that's because it has the worst backing, which places it likely to fall apart the soonest. Until that unknown time (it might last quite well) it should resist abrasion quite well. It has the widest range of colours and the only option for fluoro colours. It is the lightest fabric, and absorbs the least water.

1000D nylon with PU backing. The most expensive option and a moderate weight, will certainly last the longest. Comes with a water repellent coating which (while it lasts) almost completely prevents light falling water (eg, rain) being absorbed, and when submerged, to not much more water than the cheap nylon absorbs. More water can be forced into it, but still a reasonable amount. Dries quite quickly. Black only.

600D polyester with PU backing. Light weight with a much better backer than the 420D nylon, meaning it should hold together longer and resist tearing better than the cheap nylon. May absorb the same amount of water as the PVC backed version (still much less than polycotton) but the backer should keep the water on the outside. A range of colours.

600D polyester with PVC backing. The heaviest and most waterproof option, but also absorbs the most water of the three tested (still much less than polycotton) and dries the slowest (still faster than polycotton). Might work best as a waterproof layer on the butt and knees with one of the cheaper fabrics, especially if a spray-on waterproofer is used on it. A range of colours.

With the caving I do the 1000D nylon is definitely the sensible option for me (although I'd really prefer something a bit more photo-friendly than black; some brightly coloured and/or reflective strips might be a good safety precaution). For those doing less extreme caving but wanting a cheaper option for the main fabric it would make good reinforcing for knees and butt. It'll also make good bags.

For the cheap fabrics it's a hard call between the 420D nylon and the 600D polyester. Both fabrics feel quite thin, but the polyester feels much less plasticky than the nylon. The polyester has a significantly higher claimed tear strength than the nylon, probably due to its better backing which is likely to make a big difference long term – the better backing will help hold the polyester together. Polyester is generally easier to clean than nylon, and doesn't take on a permanent mud hue.

But 420D nylon is supposed to beat 600D polyester for abrasion resistance. The nylon absorbed very little water and was extremely quick to dry, the PVC backed polyester much slower (maybe partly due to water not being able to evaporate from both surfaces). Since it's the same fabric except for the backing, the PU backed polyester may absorb the same amount as the PVC backed polyester – quite a bit of water for its weight. I wish I was able to test it.

Another consideration is how much it's going to cost to sew the overalls. Bearing in mind the extra cost of zippers, Velcro, foam padding, thread, what proportion of the total cost should be spent on the fabric? And once again, the simpler the design, the easier it is to sew and the less to catch on stuff.

Still To Do

The fabrics have not been exhaustively tested. One of the shop owners suggested the best way to test them might be to just try them out. So I'll do that. I'm in the process of making a 420D nylon suit using some of the 600D polyester (PVC backing) for a double layer on the butt and knees.

Also:

A sample of the 600D polyester with PU backing really needs to be water tested.
No abrasion testing has been done. This should give an idea if the 420D nylon will hold up long term.
How well would the PVC backing last if on the outside?

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