If you're following this with a view to building the good news is that the material of choice is widely available ~ and worldwide ~ in the form of tile backing board.
Proceed with caution however, as whether these are double-sided or not depends on whether in turn they are destined for wall (yes) or floor (no).
Though available in various thicknesses, generally missing is my preferred choice in the form of 25mm... although my dream sheet as Baldrick may have said is actually available from a UK manufacturer pictured above.
It costs £17 online tho' delivery is £27... sign of the times.
For now then, we'll run with 20mm or three-quarter inch.
