A glass run channel having an elongated shape, which is mounted on a run mounting portion of a window frame of a vehicle door, guides moving up and down of a windowpane and is made of a polymer material, the glass run channel comprising: a run channel main body that forms the main part of the glass run channel, the run channel main body including, a base bottom portion which is provided at a position facing an end surface of the windowpane; an interior side wall portion which extends from a width end of the base bottom portion, an exterior side wall portion which extends from another width end of the base bottom portion, an interior seal lip, which projects toward the base bottom portion from an opening side end of the interior side wall portion and elastically contacts a first surface of the windowpane, and an exterior seal lip, which projects toward the base bottom portion from an opening side end of the exterior side wall portion and elastically contacts a second surface of the windowpane, wherein the run channel main body has a foamed part made of a foamable polymer material that includes a thermoplastic elastomer material and thermal expansion capsules, and has foaming cells which are formed by expansion of the thermal expansion capsules; characterized in that: the foamable polymer material, which forms the foamed part of the run channel main body, includes 100 parts by weight of the thermoplastic elastomer material and 0.5 to 2.0 parts by weight of the thermal expansion capsules; wherein: a water absorption rate of the foamed part of the run channel main body is adjusted to 5% or less; and the specific gravity of the foamed part of the run channel main body is 0.50 to 0.75. a run channel main body that forms the main part of the glass run channel, the run channel main body including, a base bottom portion which is provided at a position facing an end surface of the windowpane; an interior side wall portion which extends from a width end of the base bottom portion, an exterior side wall portion which extends from another width end of the base bottom portion, an interior seal lip, which projects toward the base bottom portion from an opening side end of the interior side wall portion and elastically contacts a first surface of the windowpane, and an exterior seal lip, which projects toward the base bottom portion from an opening side end of the exterior side wall portion and elastically contacts a second surface of the windowpane, a base bottom portion which is provided at a position facing an end surface of the windowpane; an interior side wall portion which extends from a width end of the base bottom portion, an exterior side wall portion which extends from another width end of the base bottom portion, an interior seal lip, which projects toward the base bottom portion from an opening side end of the interior side wall portion and elastically contacts a first surface of the windowpane, and an exterior seal lip, which projects toward the base bottom portion from an opening side end of the exterior side wall portion and elastically contacts a second surface of the windowpane, the foamable polymer material, which forms the foamed part of the run channel main body, includes 100 parts by weight of the thermoplastic elastomer material and 0.5 to 2.0 parts by weight of the thermal expansion capsules; wherein: a water absorption rate of the foamed part of the run channel main body is adjusted to 5% or less; and a water absorption rate of the foamed part of the run channel main body is adjusted to 5% or less; and the specific gravity of the foamed part of the run channel main body is 0.50 to 0.75.