Can you explain why aren't space blankets used to keep neonatal children warm?

Need access to baby: While we do need to keep these babies warm and keep their fluids in, also need access to them, so something like a space blanket can limit access and also visualization of the baby to see how they are doing. We actually in pinch will use Saran wrap to keep in heat and fluid without losing the ability to see the baby. In developing countries things like space blankets are used for growing preemies.