Pillow top mattresses can be made of memory foam, latex foam, fibers, wool, or gel but euro tops are usually made with foam or fiberfill (meaning the euro top is usually constructed with better quality materials).
In terms of appearance, a pillow top mattress looks like someone just laid a giant pillow blanket over the mattress, but it’s actually stitched onto the mattress to keep it from falling off. However, there is a slight gap between the mattress and pillow top. So it may appear thick, but it won’t be as dense.
Pillow top mattresses can feel softer than euro tops because they’re less taught on the mattress, allowing you to sink in a bit more. That being said, pillow tops also tend to shift around more as you move or change positions; however, this can be minimized by adding a mattress cover and sheets.