An egg-shaped casing of silk spun by the silkworm round itself to protect itself in its dormant stage as a pupa (chrysalis). It produces a viscose fluid made up of fibroin and a gum called sericin, together, from two sets of glands along its body. This it emits through an orifice, called a spinneret, in its head and it hardens on contact with the air to form a filament. With this it spins, layer after layer, in a figure-8 pattern round itself, forming its cocoon. This is the source of silk.

Cocoons are graded.

  1. Good cocoons: perfect for mechanical reeling.
  2. Pointed cocoons – (found rarely) not good for mechanical reeling.
  3. Extra large cocoons called cocalons (in French).
  4. Duppioni: double cocoons.
  5. Loose, transparent cocoons called soufflon (in French).
  6. Perforated or pierced cocoons.
  7. Cocoons containing dead chrysalis
  8. Rotten cocoons.
  9. Cocoons with petrified or calcinated chrysalis.