the mat forming wheels often do not have perfectly circular cross sections but a slight ovality if the manufacturing tolerance of the mat forming wheels is for example 2 mm the nip between the mat forming wheels should be at least 4 mm this distance can however be reduced when the elements 30 are made of a soft resilient material which can deform if the ovality of the mat forming wheels makes portions of elements 30 press against each in the nip the soft material in the elements 30 thus allows very thin core elements to be formed and increases also the accuracy of the whole forming process of thin core elements this ability of elements 30 to be compressed can be used to advantage in the method described with reference to fig1 by forming the nip between the mat forming wheels 1 2 that the distance between the peripheries of said wheels is less than 2 mm such a small distance will lead to that some of the moulds will be compressed by each other in the nip due to the slight ovality of the wheels by the fact that the elements 30 can be compressed by each other the mat forming wheels can be located with a nominal distance between them being less than the double tolerance value of ovality given by the manufacturer the less the distance is between the moulds on the respective mat forming wheel in the nip the less risk for losses of sap particles the risk for sap particles to bounce out of their moulds or fall out of their core elements during transfer is thus greatly reduced by the step of placing the moulds near each other.