There is no evidence to substantiate this claim. Rednose is considered the leading authority on safe sleep in Australia. They are an independent not-for-profit organisation with a goal to reduce the number of babies, toddlers and pre-schoolers who die suddenly to 0. They have a National Scientific Advisory Group that is made up of experts in the fields of infant and child safety. Based on their research, they formed the view that there is no evidence to prove a link between ‘toxic gas’ from mattresses, and Sudden Unexpected Death in Infancy (SUDI). You can read more in this article: https://rednose.org.au/article/no-evidence-to-link-toxic-gas-from-mattresses-and-sudi. You can read more about Rednose here https://rednose.org.au/page/red-nose-today