A spacer for insulating glazing units is presented. The spacer has a polymeric main body with features that include two parallel side walls that are connected to one another by an inner wall and an outer wall. The side walls, the inner wall, and the outer wall surround a hollow chamber. According to one aspect, the polymeric main body has a glass fiber content of 0 wt.-% to 40 wt.-%, to which 0.5 wt.-% to 1.5 wt.-% of a foaming agent is added to form hollow spaces that provide a weight reduction of the polymeric main body of 10 wt.-% to 20 wt.-%.