A Raman microimaging technique was used to directly observe the interfacial profile between N-isopropylacrylamide (NIPA) and polyacrylamide (PAAM) hydrogels in water. The joined hydrogels are called bigels and are synthesized by penetrating the PAAM gel into a part of the NIPA gel network. The bigel strip contains about 97 wt % water at room temperature. The study reveals how different manufacturing parameters, such as the drying time of the NIPA substrate and the diffusion time of the PAAM pregel solution into the NIPA layer, influence the properties and extent of the bigel interface. The interface becomes thicker with increased drying time. Specifically, the average interfacial thickness of the interface after 2 h of drying is about 28 mum, but increases to 156 mum after 16 h of drying time. The extent of the interface is independent of the PAAM diffusion time. The penetration of the PAAM pregel solution into the pores of the NIPA gel is completed in less than 30 min. The topography of the surface can be well characterized by a Gaussian function with the correlation length describing the size of the interfacial region.