A refrigerant line for carrying a mixture of refrigerant and lubrication oil. The line includes an inner casing made of a material impermeable to the refrigerant/oil mixture, an outer casing made of a material that is highly permeable to the refrigerant in its gaseous state, and an intermediate layer between the inner and outer casings made of a material that is high permeable to the gaseous refrigerant but that is able to retain the admixed oil. In this way, any oil contained in a refrigerant/oil mixture leaking through the inner casing is retained by the intermediate layer, while the refrigerant gas is allowed to escape through the outer two layers. The intermediate layer may retain the oil by absorption, by adsorption, or by binding of the oil.