1) Once you sign up for a card you'll be asked to create an account on the card issuer's website. This is where you'll login to check your account balance and top your card up whenever you need to. The first time you sign up you'll need to load a small amount of US Dollars on to your prepaid card and this balance will show up on your account straight away.

2) Your prepaid card will arrive in the post usually within a couple of working days of placing your order. It will contain a PIN number and instructions on how to activate the card which usually involves logging back into your account and following a few instructions. Once activated your card is ready to use. TIP: You can change your PIN by taking your prepaid card to any UK cash machine just like a regular bank card.

3) You can use your prepaid card just like you would a regular UK bank card to pay for goods and services or withdraw cash anywhere in America that accepts VISA or MasterCard. Any time you make a payment on the card, the amount (plus any applicable fees) will be deducted from your card balance. Once your balance reaches zero, you cannot spend any more until you top it up. As the card is not linked to your bank account in any way, you cannot go overdrawn; there is no overdraft or credit facility associated with your prepaid card and no monthly statements.

4) You can top-up or reload your prepaid card at any time with your standard UK debit or credit card by logging back into your online account. Most cards also allow you to top-up by phone, SMS and via the Post Office. Once you have reloaded your card your US Dollars will be available almost instantly so if you top-up in your hotel room you can withdraw the cash by the time you leave your room!

5) If you need any help or advice, or if your card is lost or stolen you can ring the 24-hour helpline provided by your card issuer. Remember: unlike cash your US Dollars cannot be stolen from a prepaid card as your balance is chip-and-pin protected.

What really makes prepaid US Dollar cards worthwhile is how much cheaper they are to use in America compared with regular bank cards. To understand why, first you have to understand a little bit about how the charges can add up when you use your regular bank card in the USA.

Firstly there's the exchange rate. If you use your UK bank card in the USA your bank will convert your British Pounds into US Dollars using their daily exchange rate at the time you make the payment. High street banks are notorious for having some of the worst exchange rates because they don't have to be competitive. Your bank will also add on transaction or point-of-sale fees which can be a fixed amount or a percentage of the total transaction value. That's a fee you have to pay your bank every time you use your card or withdraw money in the USA!

So how are prepaid US Dollar cards different? Well most card providers we compare offer far better exchange rates than UK banks (you can check their rates now in the table above) and you'll be able to plainly see the exchange rate on offer well before you top your card up each time so you know exactly how many US Dollars you'll be getting. As for the transaction fees - well there aren't any. There's no catch. For most suppliers you can use your card as often as you like in America without incurring any additional costs (although some cards do charge, and some charge for ATM withdrawals so make sure you check out our comparisons above).