yarns show a double s configuration with a limited extension in the transversal or width direction and with an extension in the warp direction depending on the desired size of the net squares in this direction and of their lengthening desired ability this configuration as well shown in the drawings allows to simultaneously reach two results i e to obtain a good bond with the warp threads as it will be seen with reference to fig2 and to allow for a lengthening and a shortening of the final net in the longitudinal or warp direction without stressing the non elastic weft yarns 10a 10h with reference to fig2 the warp threads 11a 11d are also shown said warp threads which are elastic threads preferably but not necessarily of rubber are placed each in correspondence with one weft yarn but shifted by one step so that at the sides of the elastic element or belt a weft yarn is missing right side in fig2 or a warp thread is missing left side in fig2 not shown at the right side as shown in fig2 no weft yarn is provided for in correspondence with the last warp thread 11d the term 34 correspondence 34 as used in this paragraph refers to a one to one relationship between the weft yarns and respective warp threads for example weft yarn 10e is in 34 correspondence 34 with warp thread 11a weft yarn 10f is in correspondence with warp thread 11b etc each warp thread with the exception of the belt side ones is bonded to two weft yarns having double s configurations in correspondence with the same by.