So when looking at memory foam toppers the best metric to measure quality will be the density. Not to be confused with firmness, for memory foam its density and firmness are not necessarily related. You will want to consider the feedback on firmness to try to match your own personal needs. This can be difficult because there are all sorts of body types and preferences out there, so for every topper that exists there will be people saying its too firm, and people saying its too soft. Generally speaking the heavier you are the firmer you need, as you will bottom through a topper that is too soft and it will actually provide insufficient pressure relief. Some vendors will tell you the firmness, the vendors I like will tell you its ILD, which is a metric to measure the compression for comparison of firmness. But for most youre stuck sifting through reviews and trying to get a feel for how often people say its too soft, vs too firm, and making a judgement based on that. Not easy when no one is telling you their weight and sleep position. With all that blabbering out of the way. Youre already looking a 2 very popular affordable options. Both are around 2lb density memory foam which is on the low side. There are cheaper toppers made by companies like Linenspa, but they will be even worse quality than what you are looking at. One that offers a slightly better value is This Amazon Basics gel topper which is about 2.5lb density memory foam for $75. So mediocre quality for a good price, not a terrible deal. You would just want to be sure the feedback on the firmness matches your preferences. More on reddit.com

Note that it isn’t as simple as “does it have fiber glass.” Many many mattresses use fiber glass in ways that are safe. The question is how it’s used. More on reddit.com

http://www.sleeplikethedead.com/mattress-topper-compare.html might help you. More on reddit.com

You dont. Even though it looks expanded it might be a little softer the first night, and the firmness could also be a bit uneven. It wont actually hurt anything to use it though. They also tell people this because they dont want people using it and complaining about the smell. More on reddit.com