Hickory is the hardest commonly used domestic wood for flooring … 50% harder than Red Oak. This flooring has a 3mm wear layer with a smooth surface. The hickory has been heat-treated which changes the color of the wood. It’s suitable for above and below grade installations and additionally over water-based radiant heat systems. It can be nailed, glued or floated. Natural variations and occasional knots are allowed in this grade. The finish wear-through warranty is 25 years for residential applications. The structural warranty is lifetime.