Brake actuator (100, 200, 300), comprising a housing having an inlet port for receiving a fluid, particularly compressed air (403, 405), 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 of the first chamber increases and a volume amount 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 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; characterized in that a cross-sectional area amount of the boot inner volume at the distal end section of the boot is larger than a maximum cross-sectional segment area 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 of the first chamber increases and a volume amount 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 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; characterized in that a cross-sectional area amount of the boot inner volume at the distal end section of the boot is larger than a maximum cross-sectional segment area 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 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;