Cardboard box for holding content, and a method for using such

A cardboard box for holding content comprising:

• three or more side walls and a bottom side,
• a layer of liquid and/or gas non-permeable coating,
• every side wall having on an upper end, wherein the upper end of every side wall includes a brim/collar area, the brim/collar area being folded outwards in a non-overlapping tight fitting manner to a substantially perpendicular position relative a corresponding side wall of the three or more side walls to form an even and unbroken upward facing surface of a brim encircling a complete perimeter of the cardboard box for attaching a lid foil, the cardboard box further comprising:
• a supporting encircling brim frame template configured to be entered on an underside of the cardboard box and arranged under the brim, the supporting encircling brim frame template having an opening with a close fit towards an outside of the cardboard box just underneath the brim, for sealing off a corner area of the brim,
• the supporting encircling brim frame template comprising a non-permeable coating at least on an upper side of the supporting encircling brim frame template facing an underside of the brim/collar area, and the non-permeable coating is such that the non-permeable coating can be made adhesive by heat/pressure sealing when arranged and heat/pressure sealed to the underside of the brim.