A device for delivery of a substance, wherein the substance comprises at least one of nicotine and a flavouring, the device comprising: a vapour outlet conduit for coupling to, and for fluid communication with, a vapour creation system, said vapour outlet conduit defining a fluid passage therethrough for delivery of vapour from the vapour creation system to a user wherein said vapour outlet conduit comprises a substance carrier unit region configured to accept a substance carrier unit and retain said substance carrier unit in said fluid passage; and further comprising a substance carrier unit removably located in said fluid passage in the substance carrier unit region, said substance carrier unit comprising a substance-bearing substrate configured for releasing said substance to a vapour stream as said vapour stream passes through said vapour outlet conduit, and a housing defining a passageway in which is located the substance-bearing substrate, wherein the housing comprises a first penetrable seal at a first end of the substance carrier unit and a second penetrable seal at a second end of the substance carrier unit, the penetrable seals being penetrable to permit fluid communication through the passageway; characterized in that: the vapour outlet conduit comprises first prongs arranged to penetrate the first penetrable seal at the first end of the substance carrier unit to provide a first aperture through which air and/or vapour in a downstream region of the vapour passage can pass, and second prongs arranged to penetrate the second penetrable seal at the second end of the substance carrier unit to provide a second aperture through which air and/or vapour in an upstream region of the vapour passage can pass. a vapour outlet conduit for coupling to, and for fluid communication with, a vapour creation system, said vapour outlet conduit defining a fluid passage therethrough for delivery of vapour from the vapour creation system to a user wherein said vapour outlet conduit comprises a substance carrier unit region configured to accept a substance carrier unit and retain said substance carrier unit in said fluid passage; and further comprising a substance carrier unit removably located in said fluid passage in the substance carrier unit region, said substance carrier unit comprising a substance-bearing substrate configured for releasing said substance to a vapour stream as said vapour stream passes through said vapour outlet conduit, and a housing defining a passageway in which is located the substance-bearing substrate, wherein the housing comprises a first penetrable seal at a first end of the substance carrier unit and a second penetrable seal at a second end of the substance carrier unit, the penetrable seals being penetrable to permit fluid communication through the passageway; characterized in that: the vapour outlet conduit comprises first prongs arranged to penetrate the first penetrable seal at the first end of the substance carrier unit to provide a first aperture through which air and/or vapour in a downstream region of the vapour passage can pass, and second prongs arranged to penetrate the second penetrable seal at the second end of the substance carrier unit to provide a second aperture through which air and/or vapour in an upstream region of the vapour passage can pass.