This depends on whether it is due to the blade being weak or the material being too hard. There are plenty of materials that will bend a good blade, so users shouldn’t immediately look to swap them out before investigating. If the current blade and the backup flex during the same session, then they are either too weak or the material is too strong. Be wary of the thickness since that will determine how much a blade can take when buying utility knives. Too much flexing is a danger even when you have a foolproof lock mechanism.