MnSi is a metallic itinerant magnet whose noncentrosymmetric crystal structure (B20 symmetry) induces a small chiral interaction between magnetic moments that results in a long-wavelength (180 Å) helical order. It is famous for its enigmatic partial magnetic order with the propagation vector of the helical order having a fixed magnitude (2π/180 Å) but random direction. It may underlie its anomalous specific heat, thermal expansion, electrical resistivity and other bulk properties. I will show that frustrated nature of magnetic interactions in cubic helical magnets such as MnSi naturally and generically induces complex spin arrangements, which we call triple helices. These are similar to double helices of the liquid crystal blue phases and their calculated neutron scattering spectra show all salient characteristic of the experimentally observed partial order. The triple helices do not disappear on heating via a sharp phase transition, but melt gradually, thus inducing a very unusual temperature dependence of all bulk properties influenced by magnetism, i.e. electrical resistivity, specific heat, thermal expansion, etc.