Color shifting multilayer polymer fibers and security articles containing color shifting multilayer polymer fibers

Polymer fibers are formed with concentric alternating layers of different polymer materials. The layers pairs have cross-sectional thicknesses selected for reflecting light at a selected visible wavelength. A cross-sectional dimension of the core is at least ten times an average of the selected thicknesses of the alternating layers. Some articles formed by the fibers are formed by attaching one fiber to another: the color of the fibers at the point of attachment is different from the colors of the fibers elsewhere. The fibers may be deformed to change its color properties by elongating the cross-section of the polymer fiber along a first cross-sectional axis. In some embodiments, the fibers are polarization sensitive.