It took some time to track these down, having heard about them, as I couldn't find them in the shops. I tried using disposable changing mats which are similar, but they were too small and moved around because there is no way of securing them (mind you I didn't put them under the sheet which might have helped a little!). Glad I made the effort to find these though; they have proved very useful - perfect for putting on the bed during daytime naps 'just in case'. (Haven't got as far as nighttime without nappies yet, but I'm sure they will be even more invaluable then!). They are supposed to go under the sheet with 'wings' that fit under the matress to secure them in place, but I don't always bother as they are plenty big enough and my son sleeps quite happily on top of one. A towel over it makes it softer and, to me, is preferable to having to strip the bed and wash the sheets! I did feel slightly guilty on the environment front and wondered about buying a washable version, however these will last for ages if they are not 'used'. They are also compact enough to send off to the childminder or take away on holiday easily. These are very reasonably priced compared to some so I'm glad bought them. Highly recommended!