The mattress is firm when I lay down.  But, then my body sinks too much into the mattress after a few hours of sleep, making it look like a spongy mattress.  It would then become firm again, once I get off from the bed.  
The responsiveness of the foam is less.  I'm  a male of 5.8" , 79kgs.  The mattress might suit light-weighted people and kids.