Scientific Anglers Fly Line Backing 30lb Test - The Scientific Anglers Fly Line Backing is built with a smaller diameter for more capacity. This backing is built with advanced 3M technology that has allowed 3M to create the small diameter backing without losing the inherent strength of the backing material. We stock this backing in 100 yard spools in 30 pound test and 20 pound test. The colors available are white and orange.