Abstract: A stiffening device for filter hoses of square crosssection includes two substantially identically shaped wires or strips. Each wire or strip is bent along a single plane repeatedly substantially at right angles to each other to form a zig-zag configuration having alternate longitudinally and transversely extending portions. The length of each of the transversely extending portions correspond to the diagnonal measurement of the hose. The two wires or strips are connected with each other at the centre points of the transversely extending portions and at right angles to the individual plane of those portions.