I live in Spain,
Since building materials have different brand names here and in the US i´d like to know exactly what you guys call ceiling tile, there are two products i find here easily, one is dry wall material 13mm thick (1/2 inch) this comes in the standard wall size and a smaller one that is like 2x3 feet. The other material is harder and thicker with no paper backing it´s just formed clay, on one side it has a pattern and the back side is smooth. This one is rigid and from what i´ve seen not totally straight.

thanks,

Diego