A segment (1) for forming part of a flexible blanket for protection or stabilisation of underwater structures and pipe lines, unstable beds and embankments, the blanket comprising a plurality of segments (1) arranged in one or more layers each one segment in height, the segments of the or each layer being disposed substantially contiguously at least at a median zone of their height dimension, each segment tapering substantially regularly from a maximum cross-section at said median zone (2) to a minimum cross section at one or both ends thereof and each segment being so bonded to each adjacent segment in the region of their respective median zones that the segments are held substantially contiguously but are free to pivot relative one to another about the bond in so far as is permitted by said taper, the arrangement of the tapes being such that each segment is capable of pivotting with more than one degree of freedom, in which each segment has a cross-section of a regular polygon of even numbered side and in which each segment is bonded to its adjacent segments by a series of flexible connecting members (5) a flexible connecting member extending from the centre of each side of the segment at the median zone (2) to the centre of the opposite side of the segment at the median zone (2), characterised in that the segment includes at least one hollow sleeve (11) extending from the centre of one side of the segment at the median zone to the centre of the opposite side of the segment at the median zone, through which said sleeve in use a flexible connecting member (5) may be passed.