Hot Chilly's MTF Midweight Tops MTF Midweight baselayer for kids is a perfect first layer for cold days. Rated a 6 it is perfect for layering in the snow or under school clothes. It's not only soft and comfortable; it is made of micro fiber polyester yarns that manage moisture. With a relaxed fit there is no binding or tightness against the body. For extra warmth, add a mid or heavy layer.