These shoe liners are the best!  The little silicon patch in the heel keeps the liner in place, and it is cut so that it doesn't show even with ballet flats.  These liners work with heeled pumps as well.  I love these liners - they are the best.  Even when wearing panty hose or trouser socks, I still wear them because they make the shoes more comfortable and keep my foot from sliding around.  I wear a size 8 or 9 shoe, and the medium fit perfectly.