Our 85A Polyurethane tube is rated to 90 psi pressure at 75F. Natural gas in polyurethane tube will result in minor effect to the tubing. This could be the tube stiffening or discoloring. Our 3/8” x ¼” PVC tube, item 1J-704-10 is rated to 100 psi pressure at 75F. Natural gas typically has little to no effect on PVC product.