Method to produce a blow moulded container with inserted mounth

Blow molded container formed by over-molding tubular insert into parison, the parison covers one end of the insert and leaves its other end extending out of the molded container giving a container with impermeable inner layer and more permeable outer layer, to hydrocarbons. Part of the container wall within the insert is removed and the thickness of the more permeable layer is reduced. A blow molded container is formed with an opening by over-molding a tubular insert into a parison. When inflated the parison covers one end of the insert and leaves its other end extending out of the molded container. The resulting container has an inner layer impermeable to hydrocarbons and an outer layer that is more permeable to hydrocarbons. Part of the container wall within the insert is removed. In the remaining part the thickness of the more permeable layer is reduced in thickness to reduce diffusion of hydrocarbons along this layer. Independent claims are included for the following: (a) An insert for use as above. (b) A fuel tank as above.