A charge-coupled device (CCD) camera was used to observe n-butane-blown low-density polyethylene (LDPE) foams at the extrusion die exit. The effects of butane content, nucleating-agent (talc) content, aging modifier (glycerol monostearate), die temperature, and die geometry on the initial expansion behavior of the foam extrudate were studied. A transparent section of the foam extrudate was found at certain die temperatures. The reasons for the existence of this transparent section and its effect on the processing conditions and material formulations are discussed. POLYM. ENG. SCI., 51:492-499, 2011. (C) 2010 Society of Plastics Engineers