In this paper, the H∞ filter design is investigated for switched T-S systems. Based on a descriptor redundancy formulation of the error dynamics, new relaxed LMI-based conditions are proposed, which are suitable when the switched filter’s modes can be asynchronous with regards to the system’s ones. Compared with previous related literature, these conditions have the advantage of being free of any dwell-time constraints. Considering the simulation of an academic example, comparisons are done regarding to previous results, placing the proposed switched T-S filter design conditions among the less conservative, and illustrating their effectiveness, even when the filter’s modes are not properly matching the system’s ones.