a multilayered lightweight building board , comprising a support core , two cover layers on the support core , where the support core is made of laterally fused - together tubes . the tubes have an inner layer , and an outer layer , where the outer layer has a softening point 10 - 90 ° c . lower than the softening point of the inner layer . the lightweight building board is made from compatible thermoplastic materials , so they can be mechanically recycled by the customary processing methods for thermoplastics .