A shock-absorbing liner for a protective helmet, for being integrated between an outer shell of the helmet and an inner surface of said helmet aimed to face the head of the user, said shock-absorbing liner comprising: - at least a first part shaped as a curved thin body and comprising protuberances extending from one side of said first part; - at least a second part (41, 42, 43) shaped as a curved thin body and comprising recesses on one side of said second part (41, 42, 43); said first part and said second part (41, 42, 43) fitting together, with said second part (41, 42, 43) covering at least a portion of said first part and said protuberances of the first part being engaged into said recesses of the second part (41, 42, 43); characterised in that: - said first part is an integrally moulded part, and said protuberances of the first part are ribs extending in height along a demoulding direction of said first part and in length along the side of said first part; said ribs being arranged in at least one primary group (71, 72, 73) in which said ribs extend in height along a same demoulding direction (X1, X2, X3) of said first part; - said second part (41, 42, 43) is an integrally moulded part, apart from said first part, and said recesses of the second part (41, 42, 43) are channels extending in depth along a demoulding direction (X1, X2, X3) of said second part and in length along the side of said second part; said channels being arranged in at least one secondary group (91, 92, 93) in which said channels extend in depth along a same demoulding direction of said second part; - the ribs of said at least one primary group (71, 72, 73) and the channels of said at least one secondary group (91, 92, 93) being sized and shaped so that, by translating said first part and said second part (41, 42, 43) one towards the other in a direction parallel to the demoulding direction (X1, X2, X3) in which said ribs of the primary group extend and the demoulding direction (X1, X2, X3) in which said channels of the secondary group (91, 92, 93) extend, said second part (41, 42, 43) matches said first part and said ribs engage into said channels. - at least a first part shaped as a curved thin body and comprising protuberances extending from one side of said first part; - at least a second part (41, 42, 43) shaped as a curved thin body and comprising recesses on one side of said second part (41, 42, 43); said first part and said second part (41, 42, 43) fitting together, with said second part (41, 42, 43) covering at least a portion of said first part and said protuberances of the first part being engaged into said recesses of the second part (41, 42, 43); characterised in that: - said first part is an integrally moulded part, and said protuberances of the first part are ribs extending in height along a demoulding direction of said first part and in length along the side of said first part; said ribs being arranged in at least one primary group (71, 72, 73) in which said ribs extend in height along a same demoulding direction (X1, X2, X3) of said first part; - said second part (41, 42, 43) is an integrally moulded part, apart from said first part, and said recesses of the second part (41, 42, 43) are channels extending in depth along a demoulding direction (X1, X2, X3) of said second part and in length along the side of said second part; said channels being arranged in at least one secondary group (91, 92, 93) in which said channels extend in depth along a same demoulding direction of said second part; - the ribs of said at least one primary group (71, 72, 73) and the channels of said at least one secondary group (91, 92, 93) being sized and shaped so that, by translating said first part and said second part (41, 42, 43) one towards the other in a direction parallel to the demoulding direction (X1, X2, X3) in which said ribs of the primary group extend and the demoulding direction (X1, X2, X3) in which said channels of the secondary group (91, 92, 93) extend, said second part (41, 42, 43) matches said first part and said ribs engage into said channels.