The Surly TPU, or Thermoplastic Urethane, tube is a tough, airtight material lighter than traditional butyl innertubes. It is designed exclusively for the Surly Molenda tire, and allowed for a custom, oversized 6.2" width that maintains its structure, even when operating at low pressures. With the TPU tube installed, you can air down your Molenda tire to maximize contact patch for better flotation, traction, and overall performance.