Is there a break in period? January 17, 2019 09:31 Updated Follow We do suggest that you give your Simba at least 30 nights to ‘bed in’ – any new mattress can feel a bit different at first. Related articles My mattress arrived, how do I set it up? What base should I put my Simba on? Do I turn my mattress over regularly? Will the mattress have a smell when I first open it? Can I clean my mattress?