According to Consumer Reports, there are four selling points mattress makers will likely tout but that may not make a difference in comfort.
Foam layers improve innersprings. The majority of innerspring mattresses in our mattress Ratings are “hybrids,” meaning they include foam on top. But on some models we’ve tested, that foam was sometimes too thin to make a difference in support. Performance varied; still, hybrid innersprings that scored well had a foam layer several inches thick.