The analysis of thin-walled rods with semiopened cross-section is performed in this article. An essential characteristic for this class of thin-walled beamlike structures is their closed but flattened profile. The unusual shape of semiopened thin-walled beams allows the efficient optimization due to wide variability of shapes. One popular application of the theory of semiopened thin-walled beams is the twist beam of the semisolid suspension.