What is the inner made of / filled with?

Hi Yulia, Thank you for your enquiry, the Baby First Deluxe Innerspring Export Size Mattress has an innerspring frame with a of open cell foam surrounding the core with a cotton removable cover over top. I hope this helps.  For further information on this or any of our other products available, if you follow the link ?https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store where one of our team experts will be happy to assist you in your product search and help answer any further questions you may have. We hope this has helped with your query.