in fig1 a double hopper system 3 , comprising at least a first hopper 1 and a second hopper 2 is shown . the first hopper 1 has a first opening 4 and a second opening 5 , the second hopper 2 has a first opening 6 and a second opening 7 . the second hopper 2 extends partially into the second opening 5 of the first hopper 1 . the first opening 4 of the first hopper 1 builds up a distribution area o with a length l and a width w , from which material flows out of the first opening 4 of the first hopper 1 . in fig1 this distribution area o is shown at a distance from the hopper system 3 for a clear picture . the dimension of the distributing area o is approximately equal with the area of the first opening 4 of the first hopper 1 , wherein the first opening 4 of the first hopper 1 has as a letterbox shaped opening at the front side . the second hopper 2 is moveably arranged with respect to the first hopper 1 , whereby the second hopper 2 can move along at least ¾ of the length of l . preferably , the second hopper 2 moves along l until a side face of the second hopper 2 arrives a side face of the first hopper 1 inside the second opening 5 of the first hopper 1 . a belt 8 or paper or foil is arranged below the first opening 4 of the first hopper 1 to collect the material leaving the first hopper 1 . the first opening 6 of the second hopper 2 has a width w ′ and a length l ′, which is approximately equal to the distributing area p ( not shown in fig1 ) of the first opening 6 of the second hopper 2 . the shape of the second hopper 2 is optimized in such a way that the powder flows out of the first opening 6 of the second hopper 2 and refills the space that has been created by the decreasing powder level in the first hopper 1 . the angle of the sidewalls of the second hopper 2 and the dimension of the first opening 6 of the second hopper 2 depend at least on the flowing behavior of the powder material ( e . g ., internal friction ). this means a shaped part of the second hopper 2 is optimized in such a way that the static pressure is minimal , the powder is free flowing and no bridge formation occurs . the filling level of the second hopper 2 has only little effects in respect to the achieved powder material on the paper . therefore , refilling the second hopper 2 is less critical and can be done on a continuous or discontinuous basis . preferably , the second hopper is kept always totally filled . preferably , length of the second hopper 2 is approximately equal or a bit smaller than the width b of the second opening of the first hopper . due to the movement of the second hopper along the length l , the second hopper 2 covers the surface of the second opening 5 of the first hopper 1 . in fig2 a part of the second hopper 2 and the first hopper 1 during the refilling procedure is shown ( side - face ). the second hopper 2 moves along the length l of the first hopper ( in the direction of the arrow in fig2 ) and material leaves the first opening 6 of the second hopper 2 to fill up the material level y to a defined material level x . if the material level x is restored again , the material of the first hopper 1 is in contact with the first opening 6 of the second hopper 2 so that no material can leave the second hopper 2 via the first opening 6 of the second hopper 2 anymore . the second hopper 2 makes preferably a continuously traversing movement in the length direction l of the first hopper 1 and back , this means perpendicular and preferably horizontal to the production direction ( the first hopper 1 makes a movement in production direction in respect to the static belt 8 or the belt 8 makes a move in production direction in respect to the static first hopper 1 ). the second hopper 2 moves preferably at a constant speed from left to right . when the right side face of the second hopper 2 ( or the first opening 6 ) reaches the right side face of the first hopper 1 , the movement stops and it start moving from the right to left again at a constant speed until the left side face of the second hopper 2 ( or the first opening 6 ) reaches the left side face of the first hopper 1 . the speed of movement of the second hopper 2 can be coupled to the speed of the moving of the first hopper 1 ( or the belt 8 ), this means on the producing speed . during the production the powder is continuously flowing out of the first opening 4 in letterbox design of the first hopper 1 , so that powder level in the first hopper 1 is lowering at a constant rate . a part of the second hopper 2 can be special shaped and comprises the first opening 6 of the second hopper 2 . the first opening 6 of the second hopper 2 builds up the distribution area p ( see fig5 , for a clear picture offset of the first opening 6 of the second hopper 2 ). the distribution area p has a length of l ′ and a width of w ′. it is preferred , that the length l ′ of the distribution area p is equal or less smaller or approximately equal to the width b of the second opening 5 of the first hopper 1 a third method to start is to fill the first hopper 1 close to the desired level and then use hopper 2 to adjust it exactly to the desired powder level x . fig3 shows a detail part of the first hopper 1 . a surface s is in contact with the belt 8 . a material is inside of the first hopper 1 , whereby only a part of the material is illustrated . in a preferred embodiment a letterbox opening 20 ( 20 is part of fig4 ) is built up . fig4 shows schematically in detail a part of the first hopper 1 with a part of the second hopper 2 ( dashed lines ) in side view . the first opening 4 of the first hopper 1 is designed as letterbox 9 with a letterbox opening 20 , a surface s and a vibrating blade 10 on the top side . the vibrating blade 10 and the form of the first opening 4 of the first hopper 1 improve a homogenous flowing behavior of the powder . among other things due to the letterbox opening 20 and the vibrating blade 10 the material can be distributed very homogeneously on the belt 8 in transport direction 11 . it should be noted , that the distribution area o could be a bit greater than an area built up by the first opening 4 of the first hopper 1 . due to a distance between first opening 4 of the first hopper 1 and the belt 8 and / or the use of a vibrating means 10 , powder could be distributed in distribution area o . the second hopper 2 extends into the second opening 5 of the first hopper 1 . if the material level of the first hopper 1 conforms to the defined material level x , the first opening 6 of the second hopper 2 is in contact with the material of the first hopper 1 . in fig5 the first hopper 1 and the second hopper 2 are shown . the second opening 7 of the second hopper 2 has a width b ′. the first opening 6 of the second hopper has a width w ′ and a length l ′, whereby the length l ′ of the first opening 6 of the second hopper 2 is approximately equal to or a bit smaller than the width b of the second opening 5 of the first hopper 1 . the first hopper 1 has a total height of h 1 , which is split into a part h 2 and a surface s . due to the angular part s the width w of the first opening 4 of the first hopper 1 is different from the width b of the second opening 5 of the first hopper 1 . o distribution area , build up by the first opening of the first hopper p distribution area , build up by the first opening of the second hopper