GAF FeltBuster 48-in x 250-ft 1000-sq ft Synthetic Roof Underlayment in the Roofing Underlayment department at Lowes.com
Construction Waterproof Breathable Membrane Waterproof Building Roofing Membrane Synthetic Felt Roofing Underlayment - China Roofing Underlayment, Building Material | Made-in-China.com
Roofing Felt: Can it get wet? - Olympus Home Roofing and Solar
Synthetic Roll Roofing Underlayment 4' x 50' Repair Roll Blue Color Replaces 15# Roofing Felt Liner Lighter Weight and 10x Stronger than Felt, 25 Year Warranty!, Underlayments - Amazon Canada
4 Common Issues with Synthetic Roof Underlayment - Presidio Roofing Company