A two-layer mono-axially oriented film includes a first layer of an opaque beta-nucleated microvoided propylene-based polymer; and a second layer containing a dark pigment that is adapted for use in a thermal printer in which the thermal print-head contacts the exposed surface of the first layer. The dark pigment of the second layer pigment has a color contrasting with the color of the first layer and can contain a carbon black. The first layer includes microvoids and may be made transparent upon the application of heat by collapsing the voids of the first layer or upon the application of ultra-sonic energy.