Microbeads are solid, approximately spherical particles with diameters between one micrometre and one millimetre, distinguished from irregular powders by sphericity and a narrow size distribution rather than by composition ^[1]. Glass grades are drawn and milled, while polymer microbeads are produced by emulsion, suspension or dispersion polymerisation, in which monomer droplets or swollen particles set into spheres ^[2]. Diameter, density and surface chemistry are the defining descriptors, since buoyancy in water and retention on a filter both follow from them ^[3]. Particles of this size range are classed with microplastics when the polymer resists degradation, and that persistence separates them from mineral or glass beads of equal diameter ^[3]. Encapsulation of a colloidal core within a polymeric bead adds an internal phase without changing the outer geometry ^[2].