Before approaching targeted synthesis via Bayesian Optimization, it is important to understand the general reproducibility of the system in order to be able to set the boundaries of the optimization process correctly. Thus, using polymer P5 (PS 48 -b-PDMA 28 ), repeat experiments were carried out at set particle synthesis conditions, spanning a range of particle diameters. Results of these experiments are depicted in Figure . In the experiment, the volume fraction of the water was systematically held at 60% and 98% corresponding to what was later used as boundary values in the optimization. Total flow rates were set to 1 and 5 ml/min, respectively and the polymer concentration in THF was constant at 1mh/mL. As a direct result from these experiments, it can be observed that high flow rates favour smaller particle formation, an effect that we have observed before. When water content is low (θ water = 60%), much larger particles are observed compared to 98%, with an increase from 109 to 518 nm on average. More importantly though, the reproducibility is overall quite satisfying. For θ water = 98 %, standard deviations of less than 10% are observed. At θ water = 60 %, this increases to almost 20 %. This increase is a consequence of the higher chain mobility of BCPs at high organic solvent content, allowing the particles to rearrange quickly. This makes the kinetic trapping more difficult, and somewhat more error prone.