A shrink sleeve of expanded synthetic material, particularly for the joints of jackets on pre-insulated district heating pipes (10), is provided with a series of corrugations or folds (5) which extend over at least a half of the periphery of the sleeve. The height of the corrugations (5) varies from a maximum on the one side of the sleeve to a minimum on the other side, preferably so that the one side of the sleeve is completely smooth. The effect of the asymmetrical folds (5) is that the sleeve can easily be adapted for a joining of the pipes in a bend. The side of the sleeve which lies outermost at the bend is thus capable of being stretched without the inner side of the bend being crumpled together. Consequently, the subsequent shrinking by influence from a gas flame will be able to be effected so that the shrunken sleeve lies smoothly up against both the outer side and the inner side of the bend.