The use of a panel bottom tray made of steel considerably increases its heavy-load capacity. Steel is an elastic, hard breaking resistance material that may deform but does not break. By using aluminum foil at the panel bottom sheet you can easily get a broken panel decreasing its load resistance capacity. Steel obtains much better fire classification than steel according to UNE-EN 13501. Steel protects the panel from external aggressions such as humidity, bad use or dirt. Aluminium can easily break leaving the system vulnerable to external aggressions.