Fig 11 shows the cross-section of a sheet material that has been processed to improve its rigidity. The material is used for a roof panel on a garden storag...

(a) The process applied to the flat sheet material is corrugation. [1]

Corrugation is a forming process that creates a regular pattern of parallel ridges and valleys (folds) in a flat sheet. The sheet is passed through profiled rollers that press the wave pattern into the material, permanently deforming it into the corrugated profile.

(b) A material commonly corrugated for construction use is steel (also accept aluminium, zinc-coated steel/galvanised steel, polycarbonate, or cardboard). [1]

Corrugated steel sheet is widely used for roofing, cladding, and fencing in construction. It is often galvanised (zinc-coated) to resist corrosion.

(c) The corrugated sheet is more rigid than a flat sheet because the corrugation increases the effective depth of the cross-section perpendicular to the folds. [1]

A flat sheet has minimal depth, so it bends easily under load. The ridges and valleys of the corrugated profile give the sheet a much greater depth (measured from the peak of a ridge to the bottom of a valley). This greater depth dramatically increases the sheet's second moment of area (a measure of resistance to bending), making it behave like a series of shallow I-beams rather than a thin, flexible panel. The same material and thickness now spans much greater distances without sagging.