A laminar blank for assembling polyhedra comprising at least three arrises (2a, 2b), each of said arrises (2a, 2b) of said laminar blank comprising: [a] a first fold tab projecting from said arris, extending along the entire length of said arris to form a fold line, [b] at least two closure grooves provided in said arris, [c] a second fold-in tab projecting from the free edge of said first tab facing said arris to form at least one fold in line, [d] a closure flange projecting from the free edge of said second tab facing said first tab and extending partially along said free edge, said closure flange being arranged aligned with one of said closure grooves, [e] a third tab projecting from one of the side edges of the first tab, which has a length of at least one third the length of the adjacent arris and is foldable with respect to said first tab for cooperating with the adjacent arris, characterized in that [f] said second fold-in tab extends partially along said free edge of the first tab, [g] the arrises (2a, 2b), the closure grooves the second fold-in tab and the closure flange of said laminar blank are configured such that the second fold-in tab of a first blank can be folded over the first tab of a second blank, [h] the second fold-in tab of said second blank can be folded over the first tab of said first blank, and [i] the closure flange of said first and second blanks (1, 1') can be inserted into the corresponding closure groove of said first and second blanks (1, 1') until said closure flange projects completely from the closure groove of the blank (1,1') containing the corresponding flange which has been inserted for attaching said flange and said groove in a form-fit connection. [a] a first fold tab projecting from said arris, extending along the entire length of said arris to form a fold line, [b] at least two closure grooves provided in said arris, [c] a second fold-in tab projecting from the free edge of said first tab facing said arris to form at least one fold in line, [d] a closure flange projecting from the free edge of said second tab facing said first tab and extending partially along said free edge, said closure flange being arranged aligned with one of said closure grooves, [e] a third tab projecting from one of the side edges of the first tab, which has a length of at least one third the length of the adjacent arris and is foldable with respect to said first tab for cooperating with the adjacent arris, [f] said second fold-in tab extends partially along said free edge of the first tab, [g] the arrises (2a, 2b), the closure grooves the second fold-in tab and the closure flange of said laminar blank are configured such that the second fold-in tab of a first blank can be folded over the first tab of a second blank, [h] the second fold-in tab of said second blank can be folded over the first tab of said first blank, and [i] the closure flange of said first and second blanks (1, 1') can be inserted into the corresponding closure groove of said first and second blanks (1, 1') until said closure flange projects completely from the closure groove of the blank (1,1') containing the corresponding flange which has been inserted for attaching said flange and said groove in a form-fit connection.