Corrugated cardboard is made with two layers of kraft paper[paper?:paper sample maker cutting machine] and between them, a central corrugating (or fluting) material. The corrugations are made by softening the fluting paper with steam and then passing it over corrugating rollers. The kraft paper is then glued to each side. Thicker boards may have several layers of corrugated board glued together, although these are not widely used in food applications. The best quality board has unbleached kraft paper[kraft paper?:kraft paper cutting machine] with equal thickness either side of the fluting and uses no re-cycled material. Both bleaching and the use of re-cycled paper reduces the strength of the corrugated cardboard.
The degree of protection from mechanical damage that is provided by corrugated cardboard depends on the size and number of corrugations or 'flutes'. Smaller more numerous corrugations give rigidity to resist compression from stacking, whereas larger corrugations give a cushioning effect that resists impacts and puncturing.
Corrugated boards resist impact, abrasion and crushing damage and are therefore widely used for shipping containers for bulk foods such as dried fruit, nuts, etc.
