The flat crush resistance of laboratory-fluted corrugating medium is regarded as an important property because it is an indication of the potential flat crush resistance of corrugated fibreboard made from that medium. The corrugated medium is fluted by passing it between heated rollers. Two different test procedures are widely used: a) the fluted corrugating medium is compressed immediately after fluting (that means, within 5 s to 8 s after fluting); b) the fluted corrugating medium is conditioned for 30 min to 35 min under standard laboratory test conditions before being compressed. Since considerable advantages are claimed for both procedures and both are widely used, this International Standard describes both procedures. A method of determining the flat crush resistance of manufactured corrugated fibreboard is given in ISO 3035:1982.