number 1 in fig1 indicates as a whole a folding unit of a packaging machine ( not shown ) for continuously producing sealed gable - top packages 2 ( fig7 ) of a pourable food product , such as pasteurized or uht milk , fruit juice , wine , etc ., from a known tube ( not shown ) of packaging material . the tube is formed in known manner upstream from unit 1 by longitudinally folding and sealing a web of heat - seal sheet material . the packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength , which may comprise a layer of fibrous material , e . g . paper , or mineral - filled polypropylene material ; and a number of layers of heat - seal plastic material , e . g . polyethylene film , covering both sides of the base layer . in the case of aseptic packages 2 for long - storage products , such as uht milk , the packaging material also comprises a layer of gas - and light - barrier material , e . g . aluminium foil or ethyl vinyl alcohol ( evoh ) film , which is superimposed on a layer of heat - seal plastic material , and is in turn covered with another layer of heat - seal plastic material forming the inner face of package 2 eventually contacting the food product . with particular reference to fig8 , the web of packaging material comprises a crease pattern 10 , i . e . a number of fold lines , along which the material is folded , during the folding operation , to form a pillow pack 3 first , and then package 2 . crease pattern 10 comprises four transverse fold lines 11 , 12 , 13 , 14 . lines 11 , 12 are located close to the ends of the packaging material , and define respective top and bottom sealing areas 11 a , 12 a . crease pattern 10 comprises , in known manner , four longitudinal fold lines 15 , 16 , 17 , 18 extending between transverse fold lines 13 , 14 . crease pattern 10 also comprises a number of further fold lines 20 located in the area between line 14 and sealing area 12 a , and which form lateral flaps ( not shown ) which are subsequently folded to form a bottom wall 62 of package 2 . the pattern of fold lines 20 is known and therefore not described in detail . lines 15 , 18 are located close to lateral edges 19 of the packaging material , and lines 16 , 17 are interposed between lines 15 and 18 . crease pattern 10 also comprises a number of additional fold lines in the area between lines 11 and 13 . the additional lines comprise two fold lines 22 , 23 extending obliquely between lines 11 , 13 and converging from line 11 to line 13 ; and two fold lines 24 , 25 extending between lines 11 , 13 and converging from line 13 to line 11 . lines 22 , 23 , 24 , 25 originate at respective intersection points 15 a , 18 a , 16 a , 17 a of respective lines 15 , 18 , 16 , 17 and line 13 , and , in the embodiment shown , slope slightly in the longitudinal direction . lines 22 and 24 , the portion of line 13 between points 15 a and 16 a , and the portion of line 11 between the intersection point of lines 11 and 24 and an intersection point 11 e of lines 22 and 11 , define an area 26 . similarly , lines 23 and 25 , the portion of line 13 between points 17 a and 18 a , and the portion of line 11 between an intersection point 11 f of lines 11 and 23 and the intersection point of lines 11 and 25 , define an area 27 . lines 24 and 25 , the portion of line 11 between the intersection points of lines 24 , 25 and line 11 , and the portion of line 13 between points 16 a and 17 a , define a panel a interposed between areas 26 and 27 and in the form of an isosceles trapezium with the oblique sides converging from line 13 to line 11 . lines 22 and 23 , the portion of line 11 extending between points 11 e and 11 f , on the opposite side to panel a , and the portion of line 13 extending between points 15 a and 18 a , on the opposite side to panel a , define a panel b interposed between areas 26 and 27 and in the form of an isosceles trapezium with the oblique sides converging from line 13 to line 11 . crease pattern 10 comprises , in area 26 , two fold lines 30 , 31 originating respectively at points 15 a , 16 a and joined at a point 11 b along line 11 to define an isosceles triangle with the portion of line 13 extending between points 15 a and 16 a . similarly , crease pattern 10 comprises , in area 27 , a further two fold lines 32 , 33 originating respectively at points 17 a and 18 a and joined at a point 11 c along line 11 to define an isosceles triangle with the portion of line 13 extending between points 17 a and 18 a . lines 31 , 24 and the portion of line 11 extending between point 11 b and the intersection point of lines 24 and 11 , define the outer boundaries of a triangular panel c adjacent to panel a . and , similarly , lines 32 , 25 and the portion of line 11 extending between point 11 c and the intersection point of lines 25 and 11 , define the outer boundaries of a triangular panel d adjacent to panel a and on the opposite side to panel c . crease pattern 10 comprises three lines 34 , 35 , 36 in area 26 , and three lines 37 , 38 , 39 in area 27 ; lines 34 , 35 , 36 extend respectively from points 15 a , 16 a , 11 b to a point 45 within the isosceles triangle in area 26 ; and lines 37 , 38 , 39 extend respectively from points 17 a , 18 a , 11 c to a point 46 within the isosceles triangle in area 27 . lines 34 , 35 extend symmetrically on opposite sides of an extension of line 36 ; and lines 37 , 38 extend symmetrically on opposite sides of an extension of line 39 . there are therefore defined , in area 26 , a panel e in the form of an isosceles triangle and bounded by lines 34 , 35 and the portion of line 13 extending between points 15 a , 16 a ; a triangular panel f bounded by lines 30 , 34 , 36 ; and a triangular panel g bounded by lines 31 , 35 , 36 . similarly , there are defined , in area 27 , a panel h in the form of an isosceles triangle and bounded by lines 37 , 38 and the portion of line 13 extending between points 17 a , 18 a ; a triangular panel l bounded by lines 32 , 37 , 39 ; and a triangular panel m bounded by lines 33 , 39 , 38 . crease pattern 10 also comprises , in area 26 , a line 40 extending between intersection point 11 e of lines 11 and 22 , and a point 47 located substantially at the mid - point of line 30 . and , in the same way , crease pattern 10 comprises , in area 27 , a line 41 extending between the intersection point 11 f of lines 11 and 23 , and a point 48 located substantially at the mid - point of line 33 . there are therefore defined , in area 26 , a triangular panel n bounded by lines 22 , 40 and the portion of line 30 extending between points 15 a and 47 ; and a triangular panel o bounded by line 40 , the portion of line 11 extending between points 11 e and 11 b , and the portion of line 30 extending between points 11 b and 47 . similarly , there are defined , in area 27 , a triangular panel q bounded by lines 23 , 41 and the portion of line 33 extending between points 18 a and 48 ; and a triangular panel p bounded by line 41 , the portion of line 33 extending between points 11 c and 48 , and the portion of line 11 extending between points 11 c and 11 f . once formed , the tube of packaging material is filled with the food product for packaging , and is sealed and cut along equally spaced cross sections to form a number of pillow packs 3 ( shown in fig1 ). fig6 shows a partial view of pack 3 at the start of forming a gable portion 61 ( fig7 ) of corresponding package 2 . more specifically , packs 3 extend along an axis r , and each comprise in known manner a parallelepiped - shaped main portion 49 , and opposite end portions 50 a , 50 b ( only one shown in fig6 ) tapering from portion 49 towards respective transverse sealing strips 53 of pack 3 . portion 49 corresponds to the area of the web extending between lines 13 and 14 . more specifically , said area is folded along lines 15 , 16 , 17 and 18 to form two parallel walls 49 a ( only one shown in fig6 ), and two parallel walls 49 b ( only one shown in fig6 ) perpendicular to walls 49 a . walls 49 a correspond to the areas between lines 16 and 17 and between lines 15 and 18 ; and walls 49 b correspond to the areas between lines 15 and 16 and between lines 17 and 18 . portions 50 a , 50 b correspond to the areas of the web extending between lines 11 and 13 and between lines 12 and 14 respectively ; and strips 53 correspond to areas 11 a , 12 a of the web of packaging material . each portion 50 a , 50 b is defined by a respective pair of walls 51 a , 51 b , which are substantially in the form of an isosceles trapezium , slope slightly towards each other with respect to a plane perpendicular to the longitudinal axis r of pack 3 , and have major edges defined by respective end edges of opposite walls 49 a , and minor edges joined to each other by relative strip 53 . more specifically , walls 51 a , 51 b of portion 50 a correspond respectively to panels a , b of the web of packaging material . each pack 3 comprises , on wall 51 a , two substantially triangular portions 52 a projecting laterally on opposite sides of wall 51 a and defined by end portions of wall 51 a . similarly , each pack 3 comprises , on wall 51 b of portion 50 a , two substantially triangular portions 52 b projecting laterally on opposite sides of wall 51 b and defined by end portions of wall 51 b . portions 52 a of wall 51 a correspond respectively to panels c and d , and portions 52 b of wall 51 b correspond respectively to panels n , o and q , p of the web of packaging material . each portion 52 a of wall 51 a is connected to a corresponding portion 52 b of wall 51 b by a respective lateral face 55 . each face 55 comprises a respective surface 56 in the form of an isosceles triangle and extending upwards from respective wall 49 b ; and a respective pair of triangular surfaces 57 , 58 having a first side in common . each surface 57 , 58 also has a second side in common with surface 56 , and a third side in common with a relative portion 52 a , 52 b . faces 55 correspond respectively to the isosceles triangle defined by points 11 b , 16 a , 15 a of the packaging material , and to the isosceles triangle defined by points 17 a , 18 a , 11 c . surfaces 56 correspond respectively to panels e , h of the web of packaging material ; surfaces 57 and 58 of a first face 55 correspond respectively to panels g , f of the web of packaging material ; and surfaces 57 , 58 of a second face 55 correspond respectively to panels l , m . packs 3 are then sent to unit 1 , where they are folded mechanically to form respective packages 2 . with particular reference to fig7 , packages 2 each substantially comprise a parallelepiped - shaped main portion 60 corresponding to portion 49 of pack 3 ; and gable portion 61 , which defines the top of portion 60 and is formed by folding portion 50 a of pack 3 on unit 1 , as described in detail below . package 2 also comprises bottom wall 62 defining the bottom of portion 60 and formed by folding portion 50 b of pack 3 on unit 1 in a manner not described , by not being essential to a clear understanding of the present invention ; two parallel walls 63 , 64 ; and two parallel walls 65 , 66 extending perpendicularly between walls 63 , 64 of package 2 . more specifically , walls 63 , 64 , 65 , 66 extend perpendicularly to the plane of wall 62 . walls 63 and 64 correspond respectively to the areas of the web extending between lines 16 and 17 and between lines 15 and 18 ; and walls 65 and 66 correspond respectively to the areas of the web extending between lines 15 and 16 and between lines 17 and 18 . portion 61 comprises a wall 67 having an opening device 68 ; and a wall 69 joined to wall 68 at top sealing strip 53 . more specifically , walls 67 and 69 are each in the form of an isosceles trapezium , slope with respect to walls 63 , 64 , 65 and 66 , converge towards top strip 53 , extend at their respective major bases from respective walls 63 and 64 , and are joined at their respective minor bases adjacent to top strip 53 . walls 67 and 69 correspond respectively to panels a and b of the web of packaging material . portion 61 also comprises two lateral flaps 70 , 71 folded outside the volume of package 2 available for the food product , and extending along extensions of , and obliquely with respect to , respective walls 65 , 66 . more specifically , each flap 70 , 71 is triangular and defined by a respective oblique side of wall 67 , by a relative end 53 a , 53 b of strip 53 folded onto a relative oblique side of wall 69 , and by a relative edge 72 parallel , when folded , to relative wall 65 , 66 . more specifically , flaps 70 , 71 correspond respectively to panels d , c of the web of packaging material , and are folded to superimpose lines 32 , 31 on respective lines 23 , 22 . with particular reference to fig1 , unit 1 comprises a station 80 supplied with pillow packs 3 and for folding portion 50 a to form portion 61 of each package 2 ; a station 81 supplied with packs 3 complete with respective portions 61 , and for forming wall 62 of package 2 corresponding to each said pack 3 ; and a transfer carriage 82 for transferring pack 3 , complete with portion 61 , from station 80 to station 81 . in a manner not shown , station 81 also heats portion 61 and wall 62 , seals flaps 70 , 71 to the oblique sides of wall 69 , and seals wall 62 to portion 60 to form the complete package 2 . carriage 82 moves back and forth between stations 80 and 81 , and performs a forward movement to transfer pack 3 , complete with portion 61 , from station 80 to station 81 , and a return movement in which it is empty . station 81 is not described in detail , by not being essential to a clear understanding of the present invention . more specifically , each station 80 , 81 comprises a respective hub 84 , 85 powered by a respective motor not shown ; and a respective number of conveying devices 86 — four in the example shown — angularly integral with relative hub 84 , 85 . station 80 also comprises a folding assembly 90 which interacts with portion 50 a of each pack 3 to form portion 61 of a corresponding package 2 . more specifically , devices 86 are fixed , equally spaced angularly , to relative hub 84 , 85 , and each comprise a groove 87 facing relative hub 84 , 85 and which engages strip 53 of relative portion 50 b , 50 a ; and two paddles 88 which cooperate respectively with walls 49 a of pack 3 corresponding to walls 63 , 64 of package 2 . each device 86 at station 80 receives a pack 3 in a first angular position , in which pack 3 is inclined slightly with respect to a horizontal plane ; feeds it clockwise along a roughly ninety - degree arc to a second angular position , in which assembly 90 folds portion 50 a to form portion 61 ; and then feeds pack 3 , complete with portion 61 , along a further roughly ninety - degree clockwise arc to a third angular position , where pack 3 , complete with portion 61 , is picked up by carriage 82 and transferred to station 81 . each paddle 88 comprises , on its outer end , an edge 89 bent towards the other paddle 88 of the same device 86 to prevent pack 3 from spinning off as hubs 84 , 85 rotate . along the arc between the first and third angular position , devices 86 are set to a closed configuration in which paddles 88 cooperate with walls 49 a of pack 3 . in the first and third angular position , on the other hand , devices 86 are set to an open configuration in which paddles 88 are parted to supply station 80 with pack 3 with relative portions 50 a , 50 b to be folded , and , respectively , to supply carriage 82 with pack 3 complete with portion 61 . assembly 90 advantageously interacts , on opposite sides of axis r of each pack 3 , with portions 52 a , 52 b of pack 3 , to fold each portion 52 b onto relative surface 56 , and each portion 52 a onto relative portion 52 b to form a relative flap 70 , 71 of package 2 . with reference to fig2 to 5 , assembly 90 comprises two tools 91 , 92 for folding each portion 52 b onto relative surface 56 , and each portion 52 a onto relative portion 52 b respectively . more specifically , each portion 52 b is folded onto relative surface 56 after first being folded onto relative line 40 , 41 . tools 91 , 92 are hinged to respective output members of respective motors 105 about respective axes t parallel to the axes of rotation of hubs 84 , 85 , and are hinged to each other about a common axis s parallel to axes t . more specifically , tool 91 comprises a supporting surface 100 and two folding surfaces 101 , which cooperate respectively with wall 51 b to control the volume of portion 61 being formed , and with portions 52 b to fold them onto relative surfaces 56 . surfaces 100 and 101 are moved integrally with one another in an approach movement into contact with wall 51 b and portions 52 b respectively , and are moved with respect to one another in a folding movement in which surfaces 101 fold portions 52 b onto relative surfaces 56 . more specifically , tool 91 comprises a frame 95 fitted , on one side , with projecting surface 100 , and connected operatively , on the opposite side , to surfaces 101 ; two first levers 93 hinged to frame 95 and to the output member of relative motor 105 ; and a second lever 94 hinged to tool 92 and to frame 95 . frame 95 comprises a first member 96 fitted on one end , and on the opposite side to axis s , with projecting surface 100 ; and a second member 97 which slides with respect to member 96 and is hinged to levers 93 about an axis u parallel to axis s . levers 93 are hinged , at one end , to the output member of motor 105 about axis t , and are hinged , at the opposite end , to frame 95 about axis u . lever 94 is hinged , at one end , to tool 92 about axis s , and is hinged , at the opposite end , to frame 95 about an axis v parallel to axis s . tool 91 also comprises two third levers 99 , each of which is hinged , at one end , to relative lever 93 about axis u , and is connected operatively and movably , at the opposite end , to surface 100 and to a respective surface 101 by means of a respective connecting rod 102 . more specifically , each connecting rod 102 is l - shaped , is hinged at opposite ends to surface 100 and to a plate 107 integral with relative surface 101 , and comprises an intermediate portion , between surface 100 and relative plate 107 , which is housed inside a circular through seat formed on the end of relative lever 99 opposite axis u . members 96 and 97 are connected elastically to each other by a spring 98 , which is compressed during the folding movement of surfaces 101 , and expands when surface 100 withdraws from wall 51 b . tool 92 is similar to tool 91 , and is only described insofar as it differs from tool 91 , using the same reference numbers for identical or corresponding parts of tools 91 , 92 . tool 92 differs from tool 91 by relative surface 100 cooperating with wall 51 a at the end of the relative approach movement . surfaces 101 are the same triangular shape as portions 52 a , and fold portions 52 a onto portions 52 b , once surface 100 cooperates with wall 51 a . tool 92 also comprises two levers 94 spaced apart and which are hinged to lever 94 of tool 91 about axis s . folding assembly 90 also comprises two pressure members 110 ( fig1 and 6 ), each of which exerts pressure on a relative surface 56 , when forming relative flap 70 , 71 , to facilitate folding of portions 52 a , 52 b . more specifically , pressure members 110 are fitted to an actuating assembly 111 connected operatively to motor 105 of tool 91 in known manner not shown . assembly 111 ( shown only partly in fig6 ) comprises two plates 112 , which cooperate with respective walls 49 b of pack 3 , and from which respective pressure members 110 project ; and two lever mechanisms 115 connected to motor 105 of tool 91 by a cam mechanism not shown . motor 105 and lever mechanisms 115 are so connected that , when surface 100 of tool 91 cooperates with wall 51 b , members 110 cooperate with relative surfaces 56 , and , when surface 100 of tool 91 is detached from wall 51 b , members 110 are detached from relative surfaces 56 . more specifically , pressure members 110 are preferably made of deformable plastic material , and are tooth - shaped . more specifically , each pressure member 110 comprises a flat surface 113 which cooperates with relative surface 56 ; and a surface 114 , opposite surface 113 , which tapers from relative plate 112 and cooperates with relative surfaces 57 , 58 once portions 52 a , 52 b are folded . operation of assembly 90 will now be described with reference to one pack 3 , and as of a start instant in which pack 3 is supplied to station 80 of unit 1 . more specifically , inside a relative device 86 in the first angular position , pack 3 , positioned with axis r sloping slightly with respect to a horizontal plane , is housed with strip 53 inside groove 87 , and with walls 49 a gripped by paddles 88 . rotation of hub 84 moves device 86 into the second angular position , in which pack 3 is adjacent to assembly 90 . as hub 84 rotates , edges 89 prevent pack 3 from being spun off . in the second angular position of device 86 , motor 105 of tool 91 , by means of the cam mechanism and lever mechanisms 115 , moves each plate 112 onto relative wall 49 b of pack 3 , and surface 113 of each pressure member 110 onto relative surface 56 . next , motors 105 operate tools 91 , 92 to perform the respective approach movements of respective surfaces 100 . more specifically , surface 100 of tool 91 contacts wall 51 b of pack 3 before surface 100 of tool 92 contacts wall 51 a of pack 3 . next , motor 105 of tool 91 is operated further to perform the respective folding movements of surfaces 101 of tool 91 , and so fold portions 52 b onto relative surfaces 56 . more specifically , portions 52 b are folded with respect to wall 51 b at respective lines 22 , 23 , and are folded over along respective lines 40 , 41 to superimpose respective panels n , q on respective portions of respective panels e , h . at this point , motor 105 of tool 92 is operated to perform the respective folding movements of surfaces 101 of tool 92 , and so fold portions 52 a onto respective portions 52 b . more specifically , portions 52 a are folded with respect to wall 51 a at respective lines 24 , 25 . by the end of the folding movements , panels d , c are superimposed respectively on panels p , o , which in turn are superimposed respectively on panels q , n , which are superimposed respectively on panels h , e . once folded , panels d , c define respective flaps 70 , 71 , and have respective lines 32 , 31 superimposed on respective lines 23 , 22 . more specifically , the approach movements commence from a start position in which each member 97 rests against relative member 96 ( fig2 and 3 ). during the approach movements , motors 105 , by means of levers 93 , rotate surfaces 100 , 101 of tools 91 , 92 , integrally with one another , about axes u until surfaces 100 come to rest against walls 51 a , 51 b of pack 3 . during the approach movements , members 96 , 97 of frames 95 also move integrally with one another . once the approach movements are completed , motors 105 , by means of levers 93 , rotate levers 99 and members 97 of tools 91 , 92 further with respect to relative axes u , t , thus compressing springs 98 of tools 91 , 92 . rotation of levers 99 rotates connecting rods 102 of tools 91 , 92 with respect to relative surfaces 100 , and so , by means of plates 107 , rotates the pairs of surfaces 101 with respect to relative surfaces 100 . by the end of the folding movements , ends 53 a , 53 b are detached slightly from the oblique sides of wall 69 , and faces 55 are detached slightly from surfaces 56 to permit heating and sealing at station 81 . once the folding movements are completed , motors 105 are operated in reverse to first withdraw members 110 from surfaces 56 , then surfaces 101 from flaps 70 , 71 , and finally surfaces 100 from walls 67 , 69 . in the course of the above withdrawal movements , the previously compressed springs 98 expand to restore relative members 97 to the position resting against relative members 96 . at this point , pack 3 , complete with portion 61 , is moved by hub 84 , by means of device 86 , a further ninety degrees clockwise into the third angular position , where it is picked up by carriage 82 and transferred to station 81 . at station 81 , in known manner not described , by not being essential to a clear understanding of the present invention , wall 62 is formed ; ends 53 a , 53 b are first heated and then sealed to the oblique sides of wall 69 ; and faces 55 are first heated and then sealed to wall 69 . the advantages of assembly 90 and the method according to the present invention will be clear from the foregoing description . in particular , assembly 90 provides for fast formation of portion 61 , by operating simultaneously on opposite sides of pack 3 . moreover , formation of portion 61 by assembly 90 is highly repeatable , on account of members 110 being controlled by motor 105 of tool 91 by means of the cam mechanism . finally , assembly 90 provides for a high - quality surface finish of portion 61 by forming portion 61 by successively folding panels of the web of packaging material along relative fold lines . as opposed to being deformed , the panels are therefore simply folded along the fold lines , thus preventing any impairment in the finish of walls 67 , 69 and flaps 70 , 71 . clearly , changes may be made to assembly 90 and the method as described herein without , however , departing from the protective scope defined in the accompanying claims .