I don't use foil until the meat is done. For instance 203 for a pork butt then wrap in foil, beach towel and put it in a cooler for at least an hour if not 2 -3 hours.
I've had them in the cooler for 4 hours and they were still in the 180 degree range.
If you use it to get the meat up to temp I feel that it holds in too much moisture and causes the meat to get that boiled meat taste.