We report on trials which measured the selectivity of haddock (Melanogrammus aeglefinus) and plaice (Pleuronectes platessa) in codends made from netting materials classified by the manufacturers as low, medium and high tenacity. We measured the twine bending stiffness, thickness and tenacity (as defined by Klust, 1982) of the netting materials and investigated which of these most influenced codend selection. For haddock, only twine bending stiffness affected selection, with 150 decreasing as bending stiffness increased. For plaice, none of the twine variables affected 150, but they all influenced selection range. Increasing mesh size increased the 150 of both species, whilst increasing catch size increased haddock 150 but decreased plaice 150. As bending stiffness is difficult to measure, a proxy is required that quantifies the resistance of meshes to opening and that can be reported in future selectivity studies. Crown (C) Copyright 2015 Published by Elsevier B.V. All rights reserved.