Cut a piece of clean flannel about eight inches square. Put this (after making a small hole in the centre) over the top of a glass tumbler, pressing the flannel down to half or more of the depth of the tumbler. Then bind the flannel fast to the tumbler with a tape or cord. When ice is put into this flannel cup, lay over it another piece of clean flannel, three or four inches square. So covered, it will keep for hours, even in warm weather.