Carbon fibre and stainless steel were chosen as materials for making the SFM as one of the key properties of both is the ability to resist an effect called 'creep'. Creep is an impact associated with products manufactured from polymeric materials (plastics) whereby any increased strain - even that under the recommended level. It occurs as a function of time through extended exposure to levels of stress that are below the yield strength of the material. Given sufficient time, this can lead to creep rupture, the failure within a material as a result of continuously applied stress at a level below the tensile strength.  Plastic materials are particularly prone to creep rupture through exposure to static stresses. Simple answer: carbon and steel SFMs will last longer and perform better than plastic counterparts.