Brake actuator , comprising a housing having an inlet port for receiving a fluid, particularly compressed air , and a push-rod aperture , the housing arranged and configured to accommodate - a first chamber connected to the inlet port ; and - a second chamber that includes the push-rod aperture , and wherein the first chamber and the second chamber are separated by a movable separation element arranged at the housing , such that a volume amount (V1) of the first chamber increases and a volume amount (V2) of the second chamber decreases when the fluid enters the first chamber via the inlet and actuates the separation element ; the brake actuator , further comprising: - a push-rod having a proximal end connected to the movable separation element , and a distal end protruding outside the housing via the push-rod aperture ; and - a boot defining a boot inner volume (V3) for accommodating a middle section of the push-rod , the boot having a proximal end section connected to the push-rod at a region proximate the proximal end of the push-rod , and a distal end section connected to the housing at the push-rod aperture ; the boot having at least one foldable boot segment in a longitudinal direction (L); characterized in that a cross-sectional area amount (A1) of the boot inner volume (V3) at the distal end section of the boot is larger than a maximum cross-sectional segment area (A2) of a first boot segment proximate the distal end section such that, in a folded state of the boot , the first boot segment is at least partially fitted inside the distal end section . - a first chamber connected to the inlet port ; and - a second chamber that includes the push-rod aperture , and the first chamber and the second chamber are separated by a movable separation element arranged at the housing , such that a volume amount (V1) of the first chamber increases and a volume amount (V2) of the second chamber decreases when the fluid enters the first chamber via the inlet and actuates the separation element ; the brake actuator , further comprising: - a push-rod having a proximal end connected to the movable separation element , and a distal end protruding outside the housing via the push-rod aperture ; and - a boot defining a boot inner volume (V3) for accommodating a middle section of the push-rod , the boot having a proximal end section connected to the push-rod at a region proximate the proximal end of the push-rod , and a distal end section connected to the housing at the push-rod aperture ; the boot having at least one foldable boot segment in a longitudinal direction (L); characterized in that a cross-sectional area amount (A1) of the boot inner volume (V3) at the distal end section of the boot is larger than a maximum cross-sectional segment area (A2) of a first boot segment proximate the distal end section such that, in a folded state of the boot , the first boot segment is at least partially fitted inside the distal end section . - a push-rod having a proximal end connected to the movable separation element , and a distal end protruding outside the housing via the push-rod aperture ; and - a boot defining a boot inner volume (V3) for accommodating a middle section of the push-rod , the boot having a proximal end section connected to the push-rod at a region proximate the proximal end of the push-rod , and a distal end section connected to the housing at the push-rod aperture ; the boot having at least one foldable boot segment in a longitudinal direction (L); <EOS>