Abstract: Encapsulated insulation product includes a mattress (1) of fibres and a cladding covering the two principal surfaces (2, 3) and the two lateral surfaces (4, 5) of the mattress, this cladding including a first covering means in the form of a band (6) which covers at least a central part of the first principal surface (2) without extending beyond it and whilst being connected thereto, and a second covering means (7-9) which covers the second principal surface (3) of the mattress, its two lateral surfaces (4, 5) and marginal parts of its first principal surface, the second covering means being connected to the first and second principal surfaces and floating freely along the opposite lateral surfaces (4, 5) of the mattress.