I usually face lather and then put the brush in a scuttle. I find if the scuttle is really hot the lather is really reduced while the initial face lathered product is really thick and the is plenty of soap still in the brush. If I keep the heat down I don't have that issue at all. I'm talking top of the line soaps here like MDC and Castle Forbes.
I think the heat just leads to break-down of the bubbles making up the lather.
