Protein shakers are available in both metal and plastic. Whilst plastic is lighter in weight, it may be considered less recyclable than metal and also less durable.
One of the advantages of a stainless steel protein shaker, such as the Free Soul's Stainless Steel Shaker, is that it is more effective at keeping your shakes cold.
It is also naturally BPA free, which means there is no plastic shaker smell and no ‘plastic’ aftertaste transferred to your drink.