An expandable composition which comprises a fluororesin and an electrically insulating whisker; an expanded article which is provided by a method comprising mixing the expandable composition with an expanding agent and effecting expansion; and a coaxial insulated cable which comprises a central electroconductive material and, arranged around the central material, an insulator layer comprising theabove expanded article. The expandable fluororesin composition can form bubbles, through the expansion, having a reduced diameter and thus the above expanded article can have bubbles being reduced inthe diameter thereof.