10 may be properly distanced thereby fluid flow between each layer of joined pair of sheets 10 may be obtained the distancing will appear only at the first end portion 11 1 and the second end portion 11 2 fluid flow may hence be provided unobstructed in the area between the first end portion 11 1 and the second end portion 11 2 however it is envisaged that other separating means may be provided along the axial extension of the sheet if the sheet are very long in order to separate pairs of sheet from each other fig1 shows a front view of the sheet 10 a flat surface 19 allows the stacking of multiple pairs of sheet 10 while distancing each pair properly from its two adjacent pairs of sheet 10 fig1 shows a stacked sheet assembly 16 u2032 which is a variation of the stacked sheet assembly 16 generally the stacked sheet assembly 16 u2032 has similar design as that of stacked sheet assembly 16 however sheet 10 u2032 utilizes other techniques than the above described sloping intermediate surfaces for distancing each pair of joined sheet 10 u2032 in particular each pair of joined sheets 10 u2032 may be stacked with other joined pair of sheets 10 u2032 by e g providing a string of hot melt adhesive transversally across an outer surface 15 u2032 of a first and a second end of each sheet 10 u2032.