Its is well known that the interstellar dust plays the most important role in which the light seen form stars suffers extinction. Conventional models assume Mie theory of light scattering with solid spheres and other shapes of silicate and graphite particles of different sizes. An extension of this theory was Effective Medium Theory (EMT) which tries to explain some of the observed interstellar properties.

Recent space probes have confirmed that the dust grains are highly porous and fluffy (i.e. aggregates or clusters) rather than having regular shapes (spherical, cylindrical or spheroidal) and homogeneous in compositionand structure. Since their is no exact theory for calculation of scattering properties of such irregular, inhomogeneous particles, recently our group has used Discrete Dipole Approximation (DDA) method and the results of this investigation will be discussed. The model uses a composite fluffy dust grain for explaining most of the average observed interstellar extinction curves and also polarization. Another parameter which needs to be constrained by the dust models is the interstellar abundances of Carbon and Silicon which is usually overestimated by the solid dust models but ourmodel predicts closer match to the observed ISM abundances. Recently, we have used our composite dust model to characterize the dust properties in about 50 different directions in our galaxy.

The Silicate dust emission features at 10 and 18 microns is also explained by our composite grain model which helps in understanding the dust characteristics in the circumstellar dust shells around stars.