The present report describes ultralow density (2~10 mg/cm3) hydrocarbon plastic (CH2) foams with a controllable micro- or nano-meter-sized lamella structure. These foams are prepared from a poly(4-methyl-1-pentene) gel with hexanol and butanol derivatives by extraction using supercritical fluid CO2. Their intended use is in laser-plasma experiments and as a laser-plasma X-ray source. Their microstructure approached to nanometer and was varied using different alcohols. The finest ultralow density foam was prepared from 2-butanol gel.