Many hospitaleros throw their hands up in dismay when pilgrims mention Compeed.
I have used it very successfully, but last year it proved to be a disaster for me.
Walking in heavy rain and mud from Roncesvalles resulted in soggy boots (not waterproof :cry: ), heavy wet socks, and great big blisters on both heels. The Compeed - which is supposed to last for a few days, even in the shower - disintegrated around the edges, stuck to the socks and tore the skin off the blisters when I took my socks off.
Compeed must go on dry skin: the instructions advise warming the plasters before you put them on to make them more adhesive: don't stretch them too far otherwise they could shrink back in the cold and the edges could curl.