Rigid polyurethane (PUR) foams as a polymer-gas composite material are widely used in construction industry, in thermal insulation for saving both heat and cold, in cars and aerospace vehicles, etc. Practical applications as well as mathematical modelling of physical and mechanical properties of neat and filled PUR foams’ require knowledge about their structure. A necessity exists to determine the characteristics of foam’s actual spatial structure without destructing the material and analysis of each structural element. In the given investigation rigid PUR foams’ are investigated with the light microscope (LM), as well as TEM and SEM microscopes with an aim to restore the spatial structure: linear dimensions of elements, spatial angles, distribution functions etc. Low density foams with spatial filling < 10% and expressed strut-like structure are considered. In such foams the main part of monolithic polymer is comprised in the structural elements: struts and knots and only a small part – in the thin polymeric walls. Neat petrochemical PUR foams, and foams obtained from sustainable source of raw materials - rape seed oil (RO) are investigated in this report also PUR foams filled with organically modified nanoclays were produced. RO polyols were synthesized by transesterication and transamidation methods, also epoxidation method were used with idea to obtain polyols with higher functionality. Renewable content in biopolyols reached up to 60%. Addition of nanoclays modifies the structure of rigid PUR foams as well as physical and mechanical properties. A methodology is applied for preparing highly porous plastic foam specimens and investigation of foam strut-like structure LM by taking images in three mutually perpendicular planes. A mathematical model is used for the determination of probability density functions of structural elements - polymeric struts’: length and angles, using LM images. Parameters of distribution functions for strut’s length and angles are calculated using experimental data for verification. Structure of neat petrochemical PUR foams, RO PUR biofoams and the PUR foams filled with organically modified nanoclays is investigated and compared.