Common waterproofing material used in cloth diapers:
PUL (Polyurethane Laminate): The most widely used waterproofing in the cloth diaper industry because of its durability. PUL is any polyester or cotton fabric that has been chemically bonded to a polyurethane (or plastic) lining. The plastic layer creates the necessary waterproofing. PUL can vary in stiffness or texture depending on the manufacturer. Some rumors have stated that the chemical process used to make PUL fabric is so harsh that it can actually destroy the buildings where manufacturing takes place. There have been no reports of chemical damage as a result of PUL creation, and PUL continues to be one of the most widely used waterproofing fabrics in cloth diapering.
- Pros: Extremely durable
- Cons: Not a breathable type of waterproofing: moisture is kept in, but air flow is kept out. Babies may benefit from diaper-free time if they experience rashes while using diapers with PUL. Chemicals are used in the creation of PUL fabrics.
- Examples: FuzziBunz, BumGenius, and many more
TPU (Thermoplastic Polyurethane): Very similar to PUL, except polyurethane (plastic) is bonded to fabric with heat instead of a chemical bond. TPU is less durable than PUL, and most manufacturers with TPU-based products offer shorter warranties on waterproofing. TPU is sensitive to heat, and can lose effectiveness if diapers are dried in the dryer on hot, dried in hot sun, or washed in hot water. TPU has not been proven to withstand over 300 washes.
- Pros: A softer and more pliable fabric. No chemicals used in the bonding process.
- Cons: Less durable and may lose waterproofing after many washes. Not a breathable type of waterproofing: moisture is kept in, but air flow is kept out.
- Examples: Grovia, Rumparooz
Nylon: Nylon is a good choice in waterproofing that is also breathable. Nylon may not be a good choice for overnight diapering, or for babies who heavily soil their diapers. Nylon diaper covers can be reused throughout the day, but if a cover begins to feel damp you should use a fresh cover.
- Pros: Breathable
- Cons: Should not be washed with hot water
- Example: Bummis Super Whisper Wrap
Wool: Wool is typically used in diaper covers paired with prefold or fitted diapers. Moisture is kept within the diaper, but the wool material is also breathable. Wool is more difficult to care for because it must be washed separately and with special "wool wash" to prevent further felting or stretching of the material, and in order to keep the wool lubricated. Wool diaper covers may only need to be laundered once a week.
- Pros: Breathable, all-natural
- Cons: Extra care necessary, and may be expensive
- Examples: Sloomb
Uncommon waterproofing used in cloth diapers:
Ultrex: Fabric is chemically bonded with a porous Teflon membrane (just like in Teflon cookware). Ultrex is less commonly found in cloth diapering products, however it is more breathable than other material. I was unable to find any cloth diaper manufacturers who currently use Ultrex in their waterproofing process.
- Pros: Breathable
- Cons: Should not be washed with hot water, and is less durable.
Spray-on waterproofing: There are a variety of products available for camping and outdoor use that can be used to waterproof fabric. These products are typically not used in cloth diaper manufacturing (if they are, you should be concerned about the reputation of the manufacturer). These products may be used in a home setting to repair damaged diapers, or to create instant waterproofing if you're on a tight budget. To use the products: spray the outside of the diaper on the printed fabric with two coatings (let dry between coatings), and let the diaper cure for 24 hrs before use or laundering.
- Pros: Cheap: you may pay around $4 to purchase this spray. Good to repair torn PUL/TPU waterproofing layers.
- Cons: Not a permanent solution, you may need to reapply product. Read the label: what are you applying?
- Examples: Atsko, Scotch Guard
A word on food-safe waterproofing for reusable snack bags
Food-safe waterproof fabrics: PUL is commonly used in food storage bags, however not all PUL has been evaluated by the FDA. Make sure that the manufacturer specifies that their waterproofing is "food safe" when purchasing any item that will be used to store food. There is a lot of controversy over what types of waterproofing are food safe. I recommend only purchasing snack bags that are specifically advertised as FDA food safe, and avoiding DIY food storage bags.
- Examples: Planet Wise reusable snack bags