We have found that the elastic on the bottom of the twin sized bedding stretches further to reach under some twin XL sized beds. Please refer to our sizing guide to measure the best fit for your mattress. Keep in mind, we currently offer a couple of different styles in twin XL size, and we do have a 14-day, no questions asked, return policy where you can return the item for a refund if it doesn't work out. Return shipping is free on all exchanges and returns. International customers are responsible for all return shipping costs.