Wool is a natural, breathable, sustainable fiber.
It is naturally flame resistant.
It helps to maintain a healthy body temperature by allowing evaporation of sweat and insulation of healthy heat. This makes it ideal for winter and summer wear. For summer, I recommend lighter weight wools when you need to have a cover on your baby. Go cover-less whenever possible.
The wool interlock I use is certified organic. It is produced and milled in the USA.
While wool requires separate washing, it does use less water, soap and energy to care for.