JBL AQUAPAD is a good quality, flexible and soft 5mm thick pad. It can be used under any aquarium. It eliminates surface tension on the glass (the possibility of glass breakage), associated with uneven bases and minor impurities under the glass/tank base. It can also be placed inside the tank to distribute the pressure caused by heavy stones placed in the aquarium.
The following dimensions of JBL Aquapad washers are available: