Wednesday, October 31, 2012

Textiles and Fibers, A-Z, pt. II: Waterproofing in cloth diapers

Like I mentioned last week, there are two necessary components of a cloth diaper system: absorbent cloth and waterproof (or water-resistant) cloth. And whether you choose a system with a separate waterproof component (usually called a 'cover' or a 'soaker,' but in the case of gDiapers is a distinctive pouch that snaps into a bloomer-cover) or with a sewn-on waterproof layer, there are lots of great options presented by the inventors and designers behind the modern cloth diaper movement.

Fortunately for you (and for me!), there are fewer textiles commonly used to provide waterproofing than there are to provide absorbency, and they can be grouped into categories that are functionally similar. Laminates and nylons provide waterproofing and feel similar to each other and perform similarly despite their being very different textiles, while fleece and wool are functionally similar in that they are water-resistant, despite being very different in some ways and requiring different styles of laundry care.

If this is information overload for you, don't worry about it! You don't have to care about this stuff to be in the cloth diaper club; not caring to learn the chemical and structural details of the textiles used in your cloth diapers does not mean you are cloth diapering the wrong way. (In fact, I think the only 'wrong way' to cloth diaper is to accept problems as part and parcel of the product instead of reaching out for help from from experienced cloth diapering moms!) But if you're a researcher or even a seamstress yourself, this hopefully comprehensive overview may strike your fancy!

Waterproof textiles

Laminates are textiles that are made waterproof by adding a layer of Thermoplastic Polyurethane (TPU) to an outer fabric that works well to complement the waterproof properties of the polyurethane. Most often, we see TPU laminated to a polyester interlock to create what is commonly called "PUL" in the cloth diapering world.

Polyurethane Laminate (PUL)
- PUL is, as mentioned above, most commonly rendered as a compound of some brand of TPU, which is a family of clear, stretchy, waterproof plastics manufactured under more than a dozen name brands, laminated to a polyester interlock or, sometimes, a thickly woven cotton. PUL can be '1 mil' or '2 mil,' which describes its thickness. Thicker PUL is alleged to be less breathable, but more durable, than thinner (1 mil) PUL. PUL is used to create the waterproofing of most pockets and AIOs as well as most wrap-style covers on the market today. 

Many sources claim that PUL was developed to be a medical-grade textile and is thus hardy under 'harsh,' sterilizing laundering conditions like regular exposure to very high heat. However, most cloth diaper manufacturers do not allow their PUL warranties to cover products that have been regularly washed in very hot temperatures--many manufacturers even specify a maximum water temperature that must be used in order to satisfy warranty conditions.

Some manufacturers have claimed that their product is made with "TPU, not PUL," but this is most likely a misunderstanding about some of the technical 'chemistry' terms involved in the world of textiles derived from plastics, which is quite a vast and confusing world!
What most manufacturers mean when they say their products make use of 'TPU' is that the manufacturing source from which they purchase their waterproof materials uses a heat (thermal) bonding rather than a chemical bonding process to laminate their outer fabric (usually a polyester interlock, but sometimes woven cotton) with TPU. However, the name "thermoplastic polyurethane" describes how this particular polyurethane (notably different from many other polyurethanes for its elasticity and its transparency) is made, not how it is bonded to its outer fabric.

So why do some PULs feel different than others? There are at least a dozen brands of that clear, stretchy TPU on the market--some are "stickier," some are smoother, and some are more textured. There are also several methods of bonding the polyurethane to the fabric outer, and each method will affect the texture of the finished compound. Additionally, some manufacturers choose to sandwich a "hidden layer" of PUL between other fabrics--the Bummis Super Whisper Wrap, for example, employs a layer of 2 mil PUL bonded to polyester on either side of the polyurethane for extra durability. This makes for a stiffer fabric, and the cover is not slick and "wipe-able," but it is extra leak-proof, and it means that no laminates touch the baby's skin.

Our newest product addition, the bumGenius Freetime, comes in proprietary colors, meaning that the color palette is commissioned by the manufacturer for its own use and cannot be found among other PUL suppliers.
Each PUL manufacturer has a contract with a particular brand of TPU (and with a particular brand of polyester interlock as well). Some cloth diaper manufacturers contract with a PUL factory and design proprietary prints and colors (which is why you can't find, say, Thirsties prints or the FuzziBunz color palette on a WAHM diaper); others just purchase wholesale and in bulk, using whatever prints and colors are available to them, and not limiting themselves to PUL manufactured at a single factory, which is why sometimes a single brand will carry prints with PUL that feels just a little different than their solid color palette or some of their other prints.

Laminates are known in the cloth diaper world for 'de-laminating,' which describes the process of the clear, plastic TPU becoming unbonded from the outer fabric. Why does this occur? Sometimes it's a reaction to too much heat exposure, and other times it's a reaction to certain chemicals. Often, though, it's just a product defect. Ever used a laminating machine to laminate paper? How many times has your finished product had a 'bubble' in it? While the process of creating PUL has been refined over the last thirty years, PUL is prone to bubbling and eventually de-laminating if the conditions under which it is bonded are not exactly, perfectly, precisely correct. That's why cloth diaper manufacturers often warranty their PUL for so long.

Pros: PUL is easily laundered, reasonably durable, and definitely waterproof. It can be manufactured in a multitude of colors and prints. Cons: Delamination does happen; fortunately, most manufacturers offer warranties to protect the customer in this event. Additionally, some children are sensitive to the chemicals used in the bonding process of a particular PUL brand or to the plastic itself; others just require more breathability than any laminate can offer.

Nylons that have been treated with a waterproofing agent are also used to create the waterproof layer of some cloth diaper systems, including the gDiapers snap-in gPouch.

Polyurethane-coated Nylon - Polyurethane-coated Nylon is simply another waterproof textile option. It is used to make old-fashioned plastic pull-on pants, like the Dappi, as well as the gDiaper snap-in gPouch. This is integral to what gDiapers terms "gBreathe technology"--because Nylon is more porous and thus more breathable than many of the polyesters used in the outer layer of the alternative, PUL. 

gPouch: coated Nylon
Interestingly, polyurethane-coated Nylon is certified 'food-safe' by the FDA (although when used for reusable food storage products, the 'shiny' side should never touch food), while PUL is not, which leads many to allege that the Nylon alternative is generally less "chemical-ly." Polyurethane-coated Nylon is certified to be mildew- and stain-resistant, although many moms find that gPouches do stain.

Pros: Coated nylon is more breathable than PUL, and there is no equivalent to the 'delamination' that is simply a risk of the PUL manufacturing procedure. Cons: Coated nylon cannot be washed in hot temperatures, which are ideal for killing the bacteria left behind on cloth diapers. Machine washing does break down the polyurethane coating more quickly than PUL is broken down; therefore, products like the gPouches do not have the life expectancy of a PUL cover.

For brevity's sake, we'll cover the water-resistant options, fleece and wool, next week. You think I had a lot to say about PUL? Just wait.

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