I have a credit card that I use quite more often then others, and obviously the magnetic strip on the back of the card has worn down quite a bit. Often, when someone slides the card it doesn't read properly and the cashier person has to manual type in my card number. Someone told me if you put the credit card in a plastic bag, such as a shopping bag from Walmart, and slide the card while its in the bag, it will read. Now when my card doesn't read, I tell the cashier to put in it in a plastic bag and it always works. What about the card being in a plastic bag makes the magnetic strip work? Thanks in advanced for any replies, my Physics professor couldn't figure it out.