Dog raincoats can be made of various materials, but some common options include polyester, nylon, or a combination of both. These materials are often treated with water-resistant coatings to help repel water and keep your dog dry in rainy conditions. Some raincoats may also have additional features such as reflective strips for increased visibility in low light conditions, adjustable straps to ensure a comfortable fit, and hoods to protect your dog's head from the rain. Ultimately, the choice of material for a dog raincoat will depend on the specific needs and preferences of the dog owner and their pet.