BD should not be an issue on THD disks. But DVD/HDDVD might. BD is at .1mm so one layer or two layers is a no brainer. But it does take care of one side. HD DVD and DVD are at .6mm 1/2 way through the disk. On one side you can only have two layers. Will it be two HD DVD, two DVD or one of each. In theory the BD side could also have DVD or HD DVD, but neither of those4 formats were built with a requirement to ignore the BD data layer. When JVC tried SS BD/DVD some DVD player had issues with the DVD side