Concrete
I was searching for a mattress that could FINALLY provide back support and not sink in the middle like those dreadful foam ones, and since I've been to Japan so many times and LOVE their hotel mattresses, I had very high hopes for my Airweave. Unfortunately, and kind of shockingly, it is actually TOO firm even for me. I still prefer it to a bed-in-a-box off-gassing boiling hot polluting piece of junk that make up most mattresses now, but I don't think I'll be keeping this much longer unless it somehow starts to have a little give to it.