A patient support apparatus comprising: a frame, an air box, and a patient support structure being supported by the frame and including a head section, a foot section, and a seat section between the head section and foot section, the patient support structure further comprising: a cushion layer, an outer ticking layer including an upper surface portion positioned to support a patient, a microclimate structure positioned within the outer ticking layer and between the cushion layer and the upper surface portion, the microclimate structure comprising an upper layer, at least a portion of the upper layer being vapor and liquid permeable, a middle layer being air permeable, and a lower layer being liquid impermeable, a first plurality of perforations extending through the upper layer of the microclimate structure in the seat section of the patient support structure, and a second plurality of perforations extending through the upper layer of the microclimate structure in the head section of the patient support structure, wherein, when the patient support structure is in a first position, the air box supplies air flow through the first plurality of perforations and the second plurality of perforations, and wherein when the patient support structure is in a second position, the air box supplies air flow through the first plurality of perforations and air flow through the second plurality of perforations is limited relative to the air flow through the first plurality of perforations and relative to the air flow through the second plurality of perforations when the patient support structure is in the first position, wherein when the patient support structure is in the second position, a crease is formed in the microclimate structure between the first plurality of perforations and the second plurality of perforations, and the air flow through the second plurality of perforations is limited by the crease, wherein the middle layer has a higher density or a lower density where the crease is formed, so as to facilitate forming of the crease when the patient support structure is moved to the second position. a frame, an air box, and a patient support structure being supported by the frame and including a head section, a foot section, and a seat section between the head section and foot section, the patient support structure further comprising: a cushion layer, an outer ticking layer including an upper surface portion positioned to support a patient, a microclimate structure positioned within the outer ticking layer and between the cushion layer and the upper surface portion, the microclimate structure comprising an upper layer, at least a portion of the upper layer being vapor and liquid permeable, a middle layer being air permeable, and a lower layer being liquid impermeable, a first plurality of perforations extending through the upper layer of the microclimate structure in the seat section of the patient support structure, and a second plurality of perforations extending through the upper layer of the microclimate structure in the head section of the patient support structure, a cushion layer, an outer ticking layer including an upper surface portion positioned to support a patient, a microclimate structure positioned within the outer ticking layer and between the cushion layer and the upper surface portion, the microclimate structure comprising an upper layer, at least a portion of the upper layer being vapor and liquid permeable, a middle layer being air permeable, and a lower layer being liquid impermeable, a first plurality of perforations extending through the upper layer of the microclimate structure in the seat section of the patient support structure, and a second plurality of perforations extending through the upper layer of the microclimate structure in the head section of the patient support structure, wherein, when the patient support structure is in a first position, the air box supplies air flow through the first plurality of perforations and the second plurality of perforations, and wherein when the patient support structure is in a second position, the air box supplies air flow through the first plurality of perforations and air flow through the second plurality of perforations is limited relative to the air flow through the first plurality of perforations and relative to the air flow through the second plurality of perforations when the patient support structure is in the first position, wherein when the patient support structure is in the second position, a crease is formed in the microclimate structure between the first plurality of perforations and the second plurality of perforations, and the air flow through the second plurality of perforations is limited by the crease, wherein the middle layer has a higher density or a lower density where the crease is formed, so as to facilitate forming of the crease when the patient support structure is moved to the second position.