1/2" Diameter x 100' Length Backer Rod Caulk Saver Foam Backer Rod for Gaps and Joints Backing Rod Concrete Filler: Amazon.com: Industrial & Scientific
Foam Backer Rod - Polar Bear Products
Titan Foam Soft Type Backer Rod - 3/8", 3600 ft. per box - Sealant Engineering Construction Supply, Inc.
3/8" Tundra Foam Open Cell Backer Rod | Open Cell Backer Rod for Hot and Cold Applications | RLOCBR38