Slim Fit: eases over the chest and shoulders, easy to layer under shirts and sweaters. Keeping it cool under sweaters, button-ups, and other layers. This undershirt is made using a super-soft cotton-modal blend with our DropTemp™ Cooling technology. DropTemp™ Cooling technology, Flat Out Seams™, Three-D Fit™. Super-soft modal (38%), cotton (57%), and elastane (5%).