Semi rigid ducting is made of solid material wrapped in insulation that comes in a variety of shapes and sizes, whereas flexible ducting is bendable and versatile. Semi rigid often comes at a higher price tag, but it can stay cleaner, trap less lint and maintain its shape better than flexible ducting. Flexible ducting is generally less expensive than semi rigid ducting, but is more prone to kinking and sagging. If you’re attaching a dryer in a tighter space, flexible ducting may be less of a hassle to work with, while semi rigid ducting can be helpful for more complicated venting paths.