The 1.8mm InnerTube is a flexable tube manufactutured from the same material as the other tubes in the Hemingway's range. The tubes have been tester down to sub-zero temperatures to ensure that they will not crack r break when cold.
The outside diameter of the 1.8mm tube is manufactured to be compatible with the 3.0mm Hemingway's Outer Tube for standard tube flies or can be used on its own for smaller tube fly patterns.