Water bag/bladder

[Colin Krusor]

The body of this water bag is made from 70D heat sealable nylon, and the cap was removed from an old TPU bladder that had a burst seam. The capacity is about 5 liters (over 11 lbs of water!), which, even when I'm carrying water for two, is more than I need. I plan to cut it down to 3 liters. I'll also add a couple of grommets at the corners. The current dry weight is 61 grams (2.1 oz).

I apologize for the quality of the photos (the camera is non-functional at the moment so these were taken with the webcam).

I've never been a big fan of hoses and bite valves, so I didn't provide for that here. I prefer to just occasionally transfer water to a small platy bottle that I keep outside my pack. I stood on it while full and hopped up and down a bit with no leaks. I think this material (which is similar to the material used for the MSR Dromedary, Hydromedary, and Dromlite bags) should be more durable than the TPU and PVC that most bladders use. Any input is appreciated.

[Travis Leanna]

Nice work! So, if you made a 2L version, it'd be around 1-1.5 ounces?

Did you just use your iron at home? If so, what setting did you use?

Is there any chemical leeching that need be worried about with heat sealable nylon?

I wonder if there is a way to use I-beam baffles to help define the shape and structure of water bladders. What I mean is, instead of having a large cylindrical blob, could a flatter, more rectangle shape be made? Think mini air mattress… these could be made to fit hydration pockets better.

[John S.]

Needs to be food grade for water carrying.

[Colin Krusor]

It's nice to have a handy axiom ("Needs to be food grade") in case a question arises about leaching from plastics, but I don't think it's in one's interest to depend on these alone to make decisions that affect one's health.

A lot of potentially deleterious things can diffuse out of a plastic into a food or beverage, and some plastics are more of a risk than others. Some plastics that are benign at room temperature and neutral pH can leach xenoestrogens or mutagens if exposed to high temperatures or extremes of pH.

The concern about contamination of food and water from plastics comes from problems associated with polycarbonates, polyvinyl chloride, and to a lesser degree, polyethylene terephthalate ("polyester") and epoxies. Bisphenol-A and phthalates are the principal contaminants of interest, although other compounds are coming under more scrutiny.

Nalgene bottles, which are food-grade, are polycarbonate and have been shown to leach BPA. Many conventional bladders for hydration packs are food-grade PVC, but leach both BPA and phthalates. Aluminum beverage cans are lined with food-grade epoxy which leaches BPA. In Japan, aluminum beverage cans are now lined with polyester due to leaching from epoxies. Polyester is thought to be the safest of the questionable plastics, but food-grade polyester can leach antimony, phosphites, and acetaldehyde (which has a bad taste but isn't very toxic).

Polyurethane is not considered one of the questionable plastics. Many companies that make hydration bladders have switched from PVC to TPU (thermoplastic urethane) due to concerns about leaching from PVC and the better mechanical properties of TPU. Most manufacturers of medical plastic containers and tubing have also switched from PVC to TPU. Heat sealable nylon is lined with TPU.

Even if there are as-yet unrecognized contaminants leaching out of TPU containers, a water bag is made to contain cold water at neutral pH, not something hot, acidic, or alcoholic that would tend to dissolve hazardous solutes in the plastic.

From a pretty basic review of current literature, I think it can be guessed that the TPU lining of heat-sealable nylon, "food grade" or not, is likely to be safer than a polycarbonate Nalgene water bottle, an aluminum soda can, or any of the widely available PVC hydration bladders.

[Colin Krusor]

Travis, I used a specialized iron with a thermostat set to 350 F. I don't know what setting would be best on a household iron. It would be simple to add baffles to keep it flatter in the pack. This is the same material that Bender uses for his sleeping pads, and adding strips of heat-sealable nylon to divide the inside of the bag into chambers, as Bender does with his down-filled pads, would be very easy.

[Travis Leanna]

Colin,
Please post any pictures and details if you end up experimenting with utilizing baffles to create a shaped bladder.

I have a few of Bender's pads, so I'm familiar with the construction–though, I have the 30D nylon which I probably wouldn't trust in a bladder. But it's held up perfectly in the sleeping pads, so who knows!

Keep us posted! I might want to test one… :)

[John S.]

The BPA scare is not really an issue in adults. The concern (and research aim) is with fetuses, infants, and children.

[Andrew Schriner]

Cool project. How did you attach the cap to the fabric?

[Colin Krusor]

The cap is heat sealed to the inside of the fabric. This cap was cut away from an old conventional water bladder made of TPU film (with heat welded seams). The heat-sealable nylon is laminated to TPU film (to permit heat sealing), so I tried pressing scraps of each material together at a series of different temperatures and I found that a strong weld was possible at about 325 F, where the melting ranges of the two films overlapped. I had actually tried this on two other occasions (heat sealing TPU film from a water bladder to a piece of heat sealable nylon) and it hadn't worked. I think the melting point of TPU can be tailored by the manufacturer and a strong weld can only be achieved between two pieces if their melting ranges happen to have significant overlap.

[max black]

Hey Colin, I'm trying to do the same type of project with the bladder and I was wondering what type of "special iron" did you use? was it the hand held rolling heat sealer kind (picture attached)???

[Roleigh Martin]

Colin,

Very fascinating post. After reading a recent report on the risk of non-BPA plastics via this link:

http://chriskresser.com/what-the-plastics-industry-doesnt-want-you-to-know

I am wondering if the MSR Dromlite or MSR Dromedary is a better hydration bladder to go with.

http://tinyurl.com/lwh7ul2

Both are made of "Cordura-500 (Nylon) / TPU" or "Cordura-200D (Nylon)/TPU".

Can you think of a safer method other than going all stainless steel such as:
http://tinyurl.com/kbzygfh

Thanks!

[Colin Krusor]

Hi Roleigh,

I think polypropylene (less common) and polyethylene (more common) containers are as unlikely to leach anything into water as stainless steel, titanium, or glass. A polyethylene bottle is a good choice, I think, for someone who is concerned about leaching. Also, polyethylene is tough, flexible, lightweight, and recyclable. And the manufacture of polyethylene is relatively environmentally benign compared to some other plastics, like PVC or polycarbonate.

It seems reasonable, I think, to put TPU into a risk category above polyethylene, polypropylene, stainless steel, titanium, and glass. But I consider TPU a low-risk family of plastics. I would place it in a lower risk category than PVC, epoxies, or polycarbonate, and probably also polyester.

These are just my interpretations of the literature I've read.

[Roleigh Martin]

Thanks Colin, what about Cordura (Nylon)? (Or is that fabric on the other side of the TPU, and it's only the TPU that water touches in the MSR bladders?)

Roleigh

[Colin Krusor]

The TPU sealing film on the nylon fabric is a barrier. The water won't be in contact with the nylon. But I see no reason to be concerned about nylon. I put it in the same category as TPU. That is, I haven't seen any research that suggests that anyone should be worried about water contact with nylon. I know that some people are concerned about nylon (ie, in nylon tea bags), but that seems hasty to me.

Also, just a note to clarify my opinion: the point of my original post about "food safe" plastics was that it doesn't seem sensible to be worried about a material unless there is concerning evidence. The blanket axiom "has to be food grade" doesn't serve us. I don't see any reason, at the moment, to doubt that polyethylene, polypropylene, silicones, TPU, and nylons are safe. So, for now, I think we should just choose these materials instead of PVC or polycarbonate for our containers and devote our attention to more significant determinants of health. Just my opinion.

[Author]

Posts