||In many interesting applications of carbon nanotubes (CNTs), it has been reported recently that CNT in the foaming systems can act as an effective nucleating agent to induce finer cell size through the heterogeneous nucleation mechanism. Cell uniformity may also be increased by this, resulting higher cell density. When considering that the nucleation density can be represented theoretically as nucleants/cm3 = (wp/ρp)*(ρblend/ Vp), low particle density and large specific area of CNTs originated from their nanostructures may induce sufficient nucleants even at small amount of CNT concentrations in the foaming system. In the present study, several PUF samples were prepared with different concentrations of CNT in the range of 0.005~0.1 phr. The cell size and cell uniformity was determined from SEM micrographs. Thermal conductivity of the samples was also investigated as a function of CNT concentrations.