This is a nice mattress bad for a sleeper sofa.  I wouldn't say it's a mattress topper, but the top of the pad has a bit of thickness to it, which makes for a more comfortable sleep.  As shown in the picture, it is not like a bed mattress pad, in that there are no sides--just four elastic straps that loop under the mattress.  This is why I'm not giving it 5 stars, because the pad can slip because it's not as secure as a mattress pad with elasticized sides.  Still, the extra padding is a nice plus, and the price was reasonable, too.

Pros: nicely padded top, reasonable price
Cons: lack of elasticized sides can cause some slippage.