Wool is environmentally sustainable. If you are cloth diapering you are already contributing to global change. But did you know that using wool products supports local farmers throughout the world? Most wool is produced organically or with low use of harmful chemicals. The processing of wool requires very little environmental impact compared to other natural fibers or man-made fibers. And, wool can be reused multiple times, and even upcycled when it is no longer needed for it's original purpose.
Wool breathes, meaning it is hygroscopic; able to absorb and release moisture as needed. In fact, most wool fiber can absorb up to three times its weight in moisture. That moisture then evaporates back into the air. This evaporative process gives wool a natural cooling and heating system, keeping sheep (and humans) warm and dry. When used as a cloth diaper cover, it wicks moisture away from your baby's skin. Keeping baby's bottom dry is key to preventing diaper rash. It is the reason why you CAN use wool in the the summer months. It is also the reason why wool is a better choice than PUL, for cloth diaper covers. PUL (polyurethane laminated fabric) is basically plastic backed fabric. While PUL is waterproof and can be autoclaved (sterilized in extreme heat), it does have a few drawbacks. PUL is designed to trap moisture and prevent it from leaking. Since PUL does not wick, moisture stays trapped against baby's skin, which can lead to irritation and rashes. PUL also traps heat in the same fashion that a disposable diaper does. It does not have the same temperature regulating properties of wool, therefore in the summer months a child can become warm from wearing a PUL cover versus a wool cover. Finally, PUL is not biodegradable. The process for manufacturing PUL covers is not environmentally friendly (it's actually quite toxic), and relies on the availability of our already taxed petroleum resources.
Wool is very poor at conducting static electricity, therefore, it is the least likely fiber to attract dirt and dust. Even dust mites hate wool. This is great for allergy sufferers, or those with sensitive skin. In fact, if someone is allergic to wool, it is likely not so much an allergy, as it is a hypersensitivity to the texture of the scales scratching on a person's skin.
Wool is naturally antibacterial, antifungal and antimicrobial. Wool inhibits the growth of microbes because those things tend to be attracted to smooth, positively charged surfaces, like those of synthetic fibers, rather than the scaly, neutrally charged surface of wool. This means that even with heavy use, wool diaper covers usually do not have ammonia build up, or other bodily odors, as they are both caused by bacterial growth. Wool will not trap and retain odors from outside sources either (pets, smoke, food), a simple 'airing out' is all that is needed. Finally, frequent washes are not necessary. Unless the garment is soiled (poop), stained, or has gone through several soaking wet diapers, you can simply leave it out to dry for a few hours.
Finally, wool is flame and fire resistant. The wool fibers are structured in such a way that if exposed to flame, they will smolder and try to extinguish themselves. Which is why wool is used to make fire blankets, rugs, curtains, bedding, mattresses, and other upholstery. This also makes it a great choice for infant and children's clothing.