The layered structure of paper is a necessary consequence of its method of manufacture by deposition of fibres from a low concentration suspension in water or air. It results in an extreme anisotropy of the in-plane and out-of-plane properties. Reported and estimated values of compressibility, strength, permeability of fluids and light transmission, in the two directions, are compared, although such comparisons are often only speculative in the absence of direct measurements of the properties of non-layered papers.
The total result of the layered arrangement of fibres is a material that is relatively dense and smooth, stiff, strong in tension, but liable to crease and delaminate. Such a combination of properties determines its performance in the four main areas of application-
1. For printing, it offers a compact, smooth surface, but poor processing strength
2. For packaging, good puncture resistance and easy creasability of board, but
poor folding endurance.
3. For hygienic and disposable products, good processing strength, but poor
softness and absorbency.
4. For barrier and filter media, good strength, but a dense packing.
Attempts are discussed that are aimed at overcoming these limitations of the layered structure.
Other sheet materials, such as felt and leather, possess a non-layered structure that strongly affects their performance. The possibilities are discussed of extending the areas of application of paper and of paper-like materials through making its structure non-layered.