Corrugated board is a combination of paper materials from which corrugated packaging is made.  Single wall corrugated board consists of three paper components:

The Outer Liner - generally high quality.

The Flute - which separates the liners and gives corrugated it's strong rigid properties.

The Inner Liner - important for strength but usually less important from the aspect of appearance.

Double wall corrugated fibreboard has an extra centre-wall and two sets of fluting, generally of different flute height and pitch.

Kraft was originally made from 100% pure wood pulp. Kraft mills now increasingly include recycled waste as a proportion of the fibre content.

Untreated Kraft is brown but has some colour variation.

Bleached Kraft is totally white.

White Top Kraft is made by only bleaching or coating the surface fibres.

Mottled Kraft is a result of the surface layer of white fibres being randomly applied, resulting in a mottled appearance.

Test

Test liners are made entirely from recycled fibres, which produce different grades.

TL3 (Test Liner 3), is superb as an inner liner and often acceptable in many situations as an outer liner.

TL2 liners offer slightly more in terms of performance and consistency of appearance and they would be specified where these requirements may be important: for example an outer liner for carrying flute graphics.

The Flute is produced by two main processes.  The first uses recycled paper with added chemicals and starch which produces a strong sheet with excellent flutability.

The second process, known as semi-chemical, reduces wood to its component fibres by the use of both mechanical and chemical means.

Flute Types

Flute in most general use is configured in five ways:

F Flute
A very fines flute, also known as micro-flute, which is used for corrugated 'cartons'.  Offers very good crush resistance and rigidity.

E Flute
A fine flute used for corrugated 'cartons'.  Benefits are excellent crush resistance and a compression strength better than solid fibreboard.

B Flute
Easily the most widely specified flute profile due to its superb robustness, good compression and its compactness minimising storage space.

C Flute
A larger flute than 'B', which offers greater compression strength, however it may be crushed more readily.  Takes up more storage space than 'B' flute.

Double Wall
A combination of two flute sizes, usually 'B' and 'C', generally specified when compression strength is more important than robustness and storage space.

One piece packs are usually able to be made with no extra set-up costs.  Die-cut packs generally require a 'tool' to be made to allow the board to be cut from flat sheets.  This tool cost is charged in addition to the pack price.

In broad terms, corrugated packaging can be categorised in two generic ways.  The trade terms are 'One piece' packs or 'Die-cut' packs.