I have done cream cheese on a pack trip to the Canyonlands-7 days, 70 miles, high desert temps...never have been sick on trail or from trail....KNocking on wood right now ;)I dont worry about cheese to much the hard kind anyway!and the way that I figure it if it doesn't pass the sniff test and/or it doesn't pass the fear test :o I dont eat it. Been sick way more often from restaurants :-[ way more :-/ But with the mylar at least I would be going out in starwars style-May the FORCE be with you all ;)