Roof Runner by CertainTeed is a lightweight, synthetic polymer-based underlayment that outperforms felt and outclasses other synthetics. Roof Runner is a durable and long-lasting synthetic roofing underlayment that provides superior protection to residential roofs. Its resistance to water, wind, ease of installation, slip-resistant surface, and durability make it a reliable and cost-effective choice for homeowners and contractors alike. Designed for use on roof decks as a water-resistant layer beneath asphalt roofing shingles, this scrim-reinforced underlayment includes a special top surface treatment that provides excellent slip resistance, even when wet.