In this article, the assay performance of 3D polyurethane (PU) hydrogel surfaces, used either plain or modified with cross linkers and additives in a direct immunoassay for IgG, is correlated with chip surface parameters such as water content and expansion, mechanical stability, hydrophilicity, thickness, and surface topography. Commercial chip surfaces ARChip Epoxy, Nexterion slide H and HydroGel are used as references. A strong correlation between assay sensitivity and physical surface parameters was found only for various hydrogels of the same chemical composition, in which cases assay sensitivity increases with decreasing hydrogel concentration as well as decreasing roughness, water content, and expansion. However, as is the case with all hydrogels tested, more hydrophobic layers with low water content are more highly reproducible from one measurement to another.