Yes, soft cotton t-shirt indeed, but you can spray the furniture polish directly on to the rag. Don't get too religious about what not to do with your humidor. I can understand not spraying anything directly on it, because before you wipe it, the theory is probably that some will seep into the opening and fumes will work their way in, but if you spray polish directly on to the rag and wipe it down well, I wouldn't worry about it.