The present invention relates to a method for reinforcing a vehicle subframe comprising one or more hollow sheet metal parts, comprising: determining at least one area on a hollow sheet metal part of a subframe with respect to specified conditions; preparing a reinforcement part which is insertable into the hollow sheet metal part at the determined area, wherein the reinforcement part comprises: a carrier having at least one hollow chamber; and a pre-foam of a foam material, which is able to expand after being heated, the pre-foam being isolated from the at least one hollow chamber and distributed at least partly on the periphery of the carrier; and installing the reinforcement part within the hollow sheet metal part at the determined area and heating the pre-foam such that it expands. The present invention also relates to a vehicle subframe reinforced by said method.