Interestingly the features of the size distribution are not shared with Nylon 6/6 which has a much more pronounced peak in the sub-micron range and very low frequencies of particles in the 10s and 100s of microns range (Supplementary Fig. ). Notably, the Nylon 6/6 shows a bimodality with a small but distinct peak at ∼200 µm, which is also qualitatively visible in the OM images. This indicates a slightly different breakage mechanism, which is further evidenced by the much broader range of solidity measured for the Nylon 6/6 sample. SEM and OM imaging reveals the elastomeric MPs as 'boulder-like', with sharp corners and shear but rough faces (Fig. , Supplementary Fig. ). FKM is a notable outlier to this trend, having a rough and lumpy surface (Supplementary Fig. ). This likely results from their different physico-chemical structure to the thermoplastics -they do not have the ability to plastically deform before breakage, due to the inability of their constituent polymers to rearrange permanently. The SEM and OM of the silicone sample clearly shows the presence of MPs that are not accounted for in the LD measurement. This may relate to the much more pronounced bimodality of the distribution.