It can be opened, but complete, with receipt, and within the return window.
Return policy - IKEA https://www.ikea.com/gb/en/customer-service/return-policy/ Return Policy 365 days to change your mind No-nonsense return policy* It's important to us that you're happy with your IKEA purchase. If you're not totally satisfied you can return it within 365 days. We will give you a full refund by the same method as your original payment for products that are returned with proof of purchase in new and unused condition and, if possible, the packaging. You can return any product, even if you assembled it, as long as it's in re-saleable condition. Unless faulty, we may refuse the return or offer an exchange or gift card only if the returns criteria are not fully met. If you purchased online and change your mind, provided you cancel your total order within 14 days of receiving it, we will also refund your delivery charge. * Terms and conditions apply Love it or exchange it Your new mattress in 90 days* It takes time for you and your new mattress to get used to each
14 days with receipt. Not sure if it has to be unopened
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