A method for forming a fluid-filled bladder, the method comprising steps of: forming a plurality of channels that extend laterally through a core formed from a polymer foam material; placing the core between a first sheet and a second sheet of a thermoplastic material; and directly bonding the first sheet to the core, directly bonding the second sheet to the core, and bonding the first sheet and the second sheet together around a periphery of the core by compressing the first sheet, the second sheet, and the core between a first portion and a second portion of a mold such that: a) the first portion of the mold contacts the first sheet adjacent to the core, thereby forming a direct bond between the first sheet and the core, b) the first portion of the mold forms a first part of the first sheet into a substantially planar first surface of the bladder, and the first portion of the mold contacts and shapes substantially all of a second part of the first sheet to form the second part of the first sheet into a sidewall of the bladder, c) the second portion of the mold contacts the second sheet adjacent to the core, thereby forming a direct bond between the second sheet and the core, d) the second portion of the mold forms the second sheet into a substantially planar second surface of the bladder that is substantially parallel to the first surface, and e) the first sheet and the second sheet are compressed together around the periphery of the core to form a peripheral bond between the second sheet and the second part of the first sheet, the peripheral bond being positioned at a location substantially coinciding with the second surface. forming a plurality of channels that extend laterally through a core formed from a polymer foam material; placing the core between a first sheet and a second sheet of a thermoplastic material; and directly bonding the first sheet to the core, directly bonding the second sheet to the core, and bonding the first sheet and the second sheet together around a periphery of the core by compressing the first sheet, the second sheet, and the core between a first portion and a second portion of a mold such that: a) the first portion of the mold contacts the first sheet adjacent to the core, thereby forming a direct bond between the first sheet and the core, b) the first portion of the mold forms a first part of the first sheet into a substantially planar first surface of the bladder, and the first portion of the mold contacts and shapes substantially all of a second part of the first sheet to form the second part of the first sheet into a sidewall of the bladder, c) the second portion of the mold contacts the second sheet adjacent to the core, thereby forming a direct bond between the second sheet and the core, d) the second portion of the mold forms the second sheet into a substantially planar second surface of the bladder that is substantially parallel to the first surface, and e) the first sheet and the second sheet are compressed together around the periphery of the core to form a peripheral bond between the second sheet and the second part of the first sheet, the peripheral bond being positioned at a location substantially coinciding with the second surface. a) the first portion of the mold contacts the first sheet adjacent to the core, thereby forming a direct bond between the first sheet and the core, b) the first portion of the mold forms a first part of the first sheet into a substantially planar first surface of the bladder, and the first portion of the mold contacts and shapes substantially all of a second part of the first sheet to form the second part of the first sheet into a sidewall of the bladder, c) the second portion of the mold contacts the second sheet adjacent to the core, thereby forming a direct bond between the second sheet and the core, d) the second portion of the mold forms the second sheet into a substantially planar second surface of the bladder that is substantially parallel to the first surface, and e) the first sheet and the second sheet are compressed together around the periphery of the core to form a peripheral bond between the second sheet and the second part of the first sheet, the peripheral bond being positioned at a location substantially coinciding with the second surface.