Water Vapor Permeability of Latex Blend Film Architectural paint is used commonly to improve appearance and protection of materials. In order to protect architectural materials, the paint should have high water resistance and water vapor permeability. However, high water vapor permeability is expected to give low water resistance. One approach to overcome that contradiction is to blend latex with high water resistance and microgel with high hydrophilicity. In this paper, the effect of mixing ratio and composition in latex and microgel blend film on water vapor permeability was investigated. We measured water vapor permeability as a function of microgel content in two blend systems, latex1/microgel and latex2/microgel. The results showed that the water vapor permeability increased as microgel content rose. The reason is that the microgel have more hydrophylic functional group on its sheath than latex.