(
High
To
Low Blu-ray) The original format for Blu-ray discs that uses an inorganic recording layer. When burned, the reflectivity is changed from high to low. Contrast with the subsequent "LTH" format (low to high reflectivity), which produced less expensive discs by using older CD/DVD manufacturing equipment. LTH discs have a shorter lifespan than HTL, and Blu-ray drives older than 2011 required a firmware update. See
Blu-ray.