While the conventional foaming techniques produced foams with cell size in the order of 100 or more micrometers, the idea of microcellular foams emerged in the early 1980s as a means to reduce the cost of mass-produced polymer items (Martini-Vvedensky et al. 1984). Microcellular foams are typically rigid structures consisting of closed-cell or open-cell sizes ranging from a few to tens of micrometers and a cell density greater than 109 cells/cm3 . The environmental friendly products are usually produced without the use of BAs such as CHCs and are widely used in the food packaging industries. The automotive industries start to replace parts with the low shrinkage, weight-reducing microcellular foams; this high strength-to-weight ratio material even lands itself in the aeronautical and transportation industries. Recent progress made on open-cell microcellular foams widen the potential applications to tissue engineering. The unique optical performances exhibited by a sheet developed by microcellular foaming technology triggered considerable interest in using these materials as reflector and diffusion sheet in liquid crystal displays by tuning the cell morphologies (Lee et al. 2011).