Coconut fibres are obtained from

A fruit's outer covering, the pericarp, develops from the ovary wall and generally separates into three distinct layers — an outer exocarp, a middle mesocarp, and an inner endocarp — each built from different tissue and serving a different purpose such as protection, fleshy or fibrous packing, or directly enclosing the seed.

The coconut shows this three-layer structure clearly, though each layer looks unusual compared with a typical fleshy fruit: the exocarp is only a thin, smooth outer skin; the endocarp is the hard, woody shell that directly encloses the seed; and the mesocarp, the thick middle layer between these two, develops as a dense mass of fibrous tissue. This fibrous mesocarp tissue is exactly what is extracted and processed commercially as coir, used to make ropes, mats, brushes, and similar fibre products.

This matches standard botanical references (e.g., NCERT biology texts and botanical descriptions of Cocos nucifera), which specifically trace coir fibre to the mesocarp layer, distinct from the smooth exocarp skin, the stony endocarp shell, and the separate seed coat around the kernel.

So coconut fibres (coir) are obtained from the mesocarp.