The expanded product of the present invention is an expanded product having a density of from 0.02 to 0.7 g / cm3, which is obtained by expanding ultra-high-molecular-weight
polyethylene having a
viscosity average molecular weight of from 300,000 to 10,000,000. This expanded product can be prepared by adding
carbon dioxide to ultra-high-molecular-weight
polyethylene in the
molten state in an extruder, and expanding the resin by
extrusion such that each of the surface temperature and the central part temperature of the resin immediately
after discharge from the die may be a predetermined temperature, while at the same time setting the
residence time and pressure of the resin at the die section to specific values. Based on these, the invention provides an expanded product with good external appearance, having a
skin layer to which the functions such as light weight, insulating property, sound absorption, low
dielectric constant,
impact absorption, flexibility and the like can be imparted without significantly deteriorating the excellent features of abrasion resistance, self-
lubrication,
impact strength, cryogenic properties and
chemical resistance that are inherent to ultra-high-molecular-weight
polyethylene; and a process for preparation of the expanded product stably.