A culvert balloon is an inflatable rubber form used in the construction and repair of culverts. It is inserted into a culvert space and inflated to shape and support concrete while it sets, creating a smooth, uniform interior. Made from durable materials, it is reusable, lightweight, and available in various sizes to match different culvert diameters. Culvert balloons help reduce labor, speed up construction, and are especially useful in hard-to-reach locations.