I used 1/4" TEMPERED 4'x8' pegboard and it was stiff enough that there
was no flexing - the spacing in the metal building was the full width
(8') but I mounted the pegboard on 2"x2" frame with a couple of 2"x2"
vertical pieces. In addition to spacing the pegboard away from the
wall, it stiffened it as well.

I did the same thing with the thick board that is white in color.
Really made it brighter in the garage.