Hi my mother in law purchased my baby a sleep suit to keep him warm when we plan to go camping. It is made of polyester. I understand polyester can cause babies to overheat and I know this is a risk factor for SIDS. Is it safe for my baby to use this?

Red Nose recommends dressing baby in clothing that will reduce the likelihood of overheating.
This includes dressing baby in clothing according to the room temperature & ensuring baby’s head & face remain uncovered.
The cooler the temperature, the wearing of more or warmer clothing is appropriate.
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep