For rigid PU, I do not suggest you add PEG into it as it will make the PU more on lower Tg, thus making it a bit elastic (depending on type of hardening agent-isocyanate that you use). Polyether and polyester polyols are the most common polyol to use. What are you focusing on? Low density rigid PU Foam? The PU additives such as the surfactant and the catalyst are playing important roles to develop the cellular structure.
Then, To clarify your enquiry about "what are focusing on ?", actually I am focusing on rigid polyurethane foam manufactoring (but currently on lab scale) which means high density, high mechanical properties and high performance of thermal insulation.