its a thin sheet of 0,5mm to cover the whole side panel and a 2mm fill in strip.
( To cut the Whole side and replace would be Beyond me :-) ) .
so 0,5mm outside as 'New' side panel , 2mm as fill in , and 1,5mm inside for added strength.

I can tell you taht it's much stiffer, even without the super strukture than it was first time I took it appart, I also added a few 1,5mm strips here and there to stiffen it up