Before working in the mattress industry, I heard the term "pillow top" used with advertising a mattress a lot. It typically alluded to some type of high-end comfort and luxury mattress. I had no idea what it was, or why I wanted it, and a trip to the mattress shop never really seemed to clear that up. You never really think about what is in your mattress, or what a pillow top might be compared to a regular top.
A pillow top is quite simple. It is a piece of polyurethane foam on top of a coil. It makes the mattress softer typically like putting a pillow over top of a coil.
Are they good? That depends a lot on the quality of the foam and the quality of the coil. The bigger the pillow top, the greater the potential for impressions and hammocking in your mattress. A really soft pillow top will often leave you with a sore back as your hips will sink to low and your spine won't be straight while you sleep, and they typically are not able to be flipped which leads to a much shorter lifespan of the mattress. They are often found to sleep quite hot as well because the polyurethane foam does not breath well and allow your body to dump heat.
The basic design itself has some merit though. By adding a little bit of cushion to your mattress, you help to accommodate side sleepers who need a little bit of cushion so they don't wake up with sore shoulders and hips. They also can be quite comfortable, which will certainly help you to sleep better providing they are not too soft and lead to back pain.
Our Marshall Coil Mattress is designed to provide the benefits of a pillow top mattress, without the downside. It can be flipped which extends the mattresses lifespan, and because it uses natural latex instead of polyurethane foam it manages to be comfortable without being too soft and sleeps much cooler because it is made of natural fibres including wool and hemp.
So is a pillow top mattress bad? Not necessarily. If it is well made with good materials it can be a great option for many sleepers. It just helps to know what it is and what the strengths and weaknesses of the design are.