second roll end 24 and from there further out of the roll 20 in the embodiment shown in fig4 the coefficient of heat transfer from the flowing heating medium to the material of the roll mantle 21 is increased in the flow direction this is accomplished by applying or producing a coating 3 on the inner face 35 of the roll mantle the coating 3 is produced by any known process e g by spraying which coating is arranged so that the thickest portion of the coating is at the initial end of the flow i e the end of the space 34 through which the heating medium enters the thickness of the coating 3 is reduced in the flow direction towards the opposite end of the roll the coating 3 is made of a suitable insulation material such as plastic or equivalent thus at the initial end of the flow where the temperature of the heating medium is highest the thickness of the coating 3 that functions as an insulation layer is the largest therefore the transfer of heat from the heating medium to the material of the roll mantle 21 is lowest at this point in a corresponding manner the thickness of the coating is reduced towards the other end of the roll whereby the transfer of heat.