Most of the cocoons studied in this project have a nonwoven porous structure, with the fibres arranged randomly in the plane of the cocoon walls. Fig. 4 shows different morphologies of nonwoven cocoons. The fibres are bonded by sericin to form a porous network (Fig. 4A). Cocoons with this structure always have a graded layer structure, with the porosity decreasing through the thickness direction from outer layer to inner layer, i.e. the level of interfibre bonding increased from outer layer to inner layer, although more sericin granules without bonding the fibres are on the outer layer; probably to promote adhesion of the cocoons in their location (Fig. 4 B–E for examples of B. mori and O. eucalypti). Actias and Cricula cocoons, which have a single and thin layer wall, have low porosity and the fibres are strongly bonded by the sericin ( Fig. 4F).