Ideally, you should try it out personally, e.g. when you go to a showroom for beds and mattresses. However, if you are shopping on the internet, this is clearly not possible. So how do you find a good memory foam topper in this situation?
One way is to search Google for memory foam topper reviews for the model you are considering. Find out why previous customers like or dislike the memory foam pad you are looking at. If you cannot find any decent reviews for that model, pick another memory foam bed topper.
You should also make sure to buy from a retailer with a lenient return policy. It is common to hear complaints of customers getting a memory foam mattress pad that is different from what they ordered. The model number may match what was written in the catalog, but the description may not match the reality. It is also common to hear customers complain that they received an old
memory foam mattress topper from the warehouse. These toppers may be yellowed, or may not decompress properly after they are unpacked. Some are outright damaged.
Technically, you want to buy a memory foam topper pad with a high density. If possible, find one with an “open structure” that allows air ventilation to remove your body heat when you lie on top of the topper. Remember that you will put the foam topper on top of your mattress, so you do not really need a thick foam pad. Double-check the dimensions of the memory foam topper against the dimensions of your bed. If the topper was made in Europe, the size may be different from what you would expect from an American measurement.
Keep in mind that you should air your memory foam mattress pad at least one week before you use it. The smell can be quite strong otherwise. If you still find the smell unbearable after a week, then you can return it to the shop.