Abstract: A foam distribution jacket (10) for containing an insulating expandable liquid foam mixture (44) prior to expansion into a space (17) between a hot water tank (22) and an outer casing (29) secured thereabout. The jacket (10) comprises a pair of sheets (11-12) which are superimposed to define a bottom trough section (13) having a straight bottom edge (15) and opposed end edges (16). A seal (17) is formed along the straight bottom edge and the opposed end edges to form the trough (13) and to interconnect the sheets (11-12). The pair of sheets (11-12) converge to a crest portion (19) at a top end section (14) thereof. An attachment hole (20) is provided in the crest of an inner one of the pair of sheets (11-12) and is adapted to attach the jacket (10) in a depending manner from a nipple (21) in a top wall (48) of a hot water tank (22). The method of insulating a surrounding space (27) formed between the hot water tank (22) and the outer casing (29) using the foam distribution jacket (10) is also described.