Here is a goal: How can I make homemade Ice packs for injuries at home?

Which way makes more sense to accomplish this goal?

OPTIONS:
(a). Mix 3 parts water and 1 part rubbing alcohol in a paper bag, it will get very cold but won't freeze hard.;
(b). Mix 3 parts water and 1 part rubbing alcohol in a ziploc bag, it will get very cold but won't freeze hard.;
(b).