These are a relatively new kind of plastic card, which are used in much the same way as credit or debit cards, with the big difference that you have to 'load' the card with funds before you can spend with it. They are a secure way of carrying money, as the card is replaceable if lost, and as it can only be used in conjunction with a PIN number then even if stolen it's difficult for a thief to make use of it. There will, however, still be exchange commissions payable when you use the card, and also usually a flat fee for cash withdrawals.The main thing to bear in mind with travel money is that while each of the above options is useful, not all are suitable for use everywhere in the world. The best advice is not to rely on a single kind of travel money, but to take a sensible mixture of cash, local currency, and plastic or cheques, to make sure you can always get local currency when you need it. Enjoy your holiday!