What is a pre-attached underlayment? Do I still need additional underlayment?

Select vinyl flooring is made with a pre-attached underlayment pad made of foam or cork. The pre-attached underlayment helps with sound absorption, insulation, and cushioning. Please refer to the manufacturer guidelines, installation instructions, and warranty information for more details and to confirm if any additional underlayment or vapor barrier is still needed prior to installation. Requirements vary based on the specific details of your project.