As compared to the monodis-persed TiO2 spheres, this polydispersed sample allows the small spheres to enter the voids among big ones, which can effectively increase the compacted density of TiO2 painting. Fig. S3(c) shows the double-layered TiO2 coatings by coating the paste-3 and paste-1 as the bottom and the top layers, respectively, we can see that the nanoparticle layer combines well with the TiO2 sphere layer.