Please be advised that this product comes with built in underlay. Using additional underlay with this product is not recommended. Please contact us for further information. Rigid Core is a super strong 100% waterproof floor, designed to be stronger and more stable than standard 100% PVC click vinyl flooring products, this flooring comes with a 1mm built in underlay for quick installation and excellent sound reduction properties. Our Naturelle Rigid Core is part of the SPC (Stone Plastic Composite) vinyl collection, this is regarded as the best click vinyl product available as the core is PVC and Limestone powder blended to formulate the toughest, most durable and waterproof flooring option available to buy.