A sinus bag is a type of plastic bag that has a handle that is reinforced for strength and is shaped like a sine curve. It is designed for use in retail stores and has a large print surface that can be used for branding or advertising. It is suitable for production in large batches and is typically used as a carrier bag. The sinus bag, with its reinforced handle and large print surface, may be a good choice for retailers who need a sturdy and attractive carrier bag.