Mainly there are three types of hairs are used in 20 inch hair extensions in the market that is human hair, synthetic hair and the third one is develop from the mixture of them. When you are looking for these you can find that there are different prices for all these three types of hairs in the market. Some of them are washable and some are not like synthetic is washable but not as often as human hairs because the fiber which is used in it can be damaged, so you must read all the washing instructions before buying one for you. There prices starts from dollar 20 to dollar 50 and it might depends on one which you choose for yourself to looks more stylish infornt of the other friends around you. These are available on different online retails stores where you can select one which you like from the list available there.