Spacer for an insulating glazing unit, which insulating glazing unit has at least two spaced glazing panes (51, 52) connected at their edges via the spacer in a mounted state in which the spacer is mounted at the edges to limit an interspace filled with gas, the spacer extending with an essentially constant cross-section (x-y) in a longitudinal direction (z), the spacer comprising a plastic body extending in the longitudinal direction (z) with two lateral side walls (11, 12) and an inner wall located on an inner side of the spacer adapted to face the gas filled interspace in the mounted state, and a diffusion barrier film 30 formed on the outer side of the spacer which faces away from the gas filled interspace in the mounted state, wherein the side walls are adapted to face the glazing panes in a width direction (x) perpendicular to the longitudinal direction (z), the side walls (11, 12) extend, in the cross section (x-y), in a height direction (y) perpendicular to the longitudinal direction (z) and the width direction (x) towards the inner side up to inner ends (11e, 12e), the side walls have a predetermined distance between their lateral outer sides at the inner ends in a state in which no external pressure force or external tensional force is applied to the side walls, the inner wall connects the side walls on the inner side of the spacer, a chamber for accommodating desiccating material is defined in cross-sectional view perpendicular to the longitudinal direction (z) on its respective lateral sides by the side walls (11, 12) and on its side facing the interspace by the inner wall, the inner wall is non-diffusion-proof allowing gas exchange between the gas filled interspace and the chamber in the mounted state, the spacer has a predetermined width in the width direction (x) corresponding to the predetermined distance, which is a value selected from a range from 10 mm to 20 mm, and a predetermined height in the height direction (y), which is a value selected from a range from 6 mm to 8 mm, and the inner wall comprises a recess portion (14rs, 14rt, 14rc) having a depth (dr) in the height direction (y) of at least 1.5 mm and a width in the width direction (x) of at least 2.5 mm and a wall thickness (dt) which is in a range 20% to 80% of the wall thickness (diw) of the other parts of the inner wall allowing to change the length of the inner wall in the width direction in response to an external pressure force or external tensional force applied to the side walls (11, 12) in the width direction (x). a plastic body extending in the longitudinal direction (z) with two lateral side walls (11, 12) and an inner wall located on an inner side of the spacer adapted to face the gas filled interspace in the mounted state, and a diffusion barrier film 30 formed on the outer side of the spacer which faces away from the gas filled interspace in the mounted state, wherein the side walls are adapted to face the glazing panes in a width direction (x) perpendicular to the longitudinal direction (z), the side walls (11, 12) extend, in the cross section (x-y), in a height direction (y) perpendicular to the longitudinal direction (z) and the width direction (x) towards the inner side up to inner ends (11e, 12e), the side walls have a predetermined distance between their lateral outer sides at the inner ends in a state in which no external pressure force or external tensional force is applied to the side walls, the inner wall connects the side walls on the inner side of the spacer, a chamber for accommodating desiccating material is defined in cross-sectional view perpendicular to the longitudinal direction (z) on its respective lateral sides by the side walls (11, 12) and on its side facing the interspace by the inner wall, the inner wall is non-diffusion-proof allowing gas exchange between the gas filled interspace and the chamber in the mounted state, the spacer has a predetermined width in the width direction (x) corresponding to the predetermined distance, which is a value selected from a range from 10 mm to 20 mm, and a predetermined height in the height direction (y), which is a value selected from a range from 6 mm to 8 mm, and the inner wall comprises a recess portion (14rs, 14rt, 14rc) having a depth (dr) in the height direction (y) of at least 1.5 mm and a width in the width direction (x) of at least 2.5 mm and a wall thickness (dt) which is in a range 20% to 80% of the wall thickness (diw) of the other parts of the inner wall allowing to change the length of the inner wall in the width direction in response to an external pressure force or external tensional force applied to the side walls (11, 12) in the width direction (x).