A method of manufacturing a separation panel made of a synthetic material, said method comprising the steps of: - providing one mould; - producing two semi-panels (101;102) by injection moulding using said mould, wherein each of said two semi-panels (101;102) comprises: ∘ a sidewall comprising an inner surface and an outer surface; ∘ a pair of parallel longitudinal walls extending from said inner surface and a pair of parallel traverse walls extending from said inner surface; and wherein both semi-panels (101;102) further comprise a symmetric plurality of partition walls extending from said inner surface, wherein: ∘ said partition walls delimitate inside cavities in each of said semi-panels (101;102); and ∘ one or more of said partition walls comprise respective openings extending through said partition walls; - arranging said two semi-panels (101;102) one against the other along said longitudinal walls and said traverse walls such that said inner surfaces of said sidewalls face each other and such that said partition walls of one of said semi-panels are in direct contact with said partition walls of the other semi-panel when said two semi-panels (101;102) are arranged one against the other, thereby forming a structure with a plurality of inside cavities connected through said openings; and - welding said two semi-panels (101;102) together along said longitudinal walls and said traverse walls, thereby forming said separation panel as a closed structure. - providing one mould; - producing two semi-panels (101;102) by injection moulding using said mould, wherein each of said two semi-panels (101;102) comprises: ∘ a sidewall comprising an inner surface and an outer surface; ∘ a pair of parallel longitudinal walls extending from said inner surface and a pair of parallel traverse walls extending from said inner surface; and wherein both semi-panels (101;102) further comprise a symmetric plurality of partition walls extending from said inner surface, wherein: ∘ said partition walls delimitate inside cavities in each of said semi-panels (101;102); and ∘ one or more of said partition walls comprise respective openings extending through said partition walls; ∘ a sidewall comprising an inner surface and an outer surface; ∘ a pair of parallel longitudinal walls extending from said inner surface and a pair of parallel traverse walls extending from said inner surface; ∘ said partition walls delimitate inside cavities in each of said semi-panels (101;102); and ∘ one or more of said partition walls comprise respective openings extending through said partition walls; - arranging said two semi-panels (101;102) one against the other along said longitudinal walls and said traverse walls such that said inner surfaces of said sidewalls face each other and such that said partition walls of one of said semi-panels are in direct contact with said partition walls of the other semi-panel when said two semi-panels (101;102) are arranged one against the other, thereby forming a structure with a plurality of inside cavities connected through said openings; and - welding said two semi-panels (101;102) together along said longitudinal walls and said traverse walls, thereby forming said separation panel as a closed structure.