Coatings must be durable and resistant to soiling, which can be achieved with porous PDRCs or hydrophobic topcoats that can withstand cleaning, although hydrophobic coatings use polytetrafluoroethylene or other similar compounds to be water-resistant. Negative environmental impacts can be mitigated by limiting use of other toxic solvents common in paints, such as acetone. Non-toxic or water-based paints have been developed. More research and development is needed.