Abstract: A method for reinforcing a selected portion of a structural part utilizes a flexible tube having a unexpanded, preferably thermally expandable resin sheath. The sheath may be limited to a selected region along the length of the flexible tube. The flexible tube is inserted through a curved passage and conforms to the geometry of the part to be reinforced. After the portion of the tube having the sheath reaches the desired location, the tube is secured in place. Upon heating, the resin expands to several times its original volume and fills the structural cavity only at that region.