An intumescent seal comprises a first body or mass of intumescent material (3) which provides a hard foam on heating and a second body or mass (4) of intumescent material which produces a soft foam on heating. An intumescent seal comprises at least one body of intumescent material (3) which produces a hard foam on heating and at least one body of intumescent material (4) which produces a soft foam on heating, the intumescent materials (3, 4) being carried by at least one of a pair of members or parts between which gap (24) is defined at least in a predetermined relative position of the two members or parts, the intumescent material being disposed so as to intumesce into the gap (24) on heating at least when the members or parts are in said predetermined position.