To size-sort microparticles of different dimensions, we designed a "staircase" positive mold for a PDMS microfluidic device (Figure ). The mold comprises a staircase with 25 µm steps, the highest resolution possible on the SLA Formlabs Form3 and the (m)SLA Prusa SLS1. Once the mold was printed, the PDMS was cast, cured, and then plasma bonded on a glass slide, following the standard replica molding procedure to prepare PDMS/Glass microfluidic devices (Figure ). The end product is made up of only 5g of PDMS and a microscope glass slide, and costs less than €2 in total.