Why does a prefab use so much memory?

I imported some .obj objects which need between 10 to 50 kb. Then I put two in a prefab an attached some script files. Both objects have the same material attached but the prefab has a size of over 150 kb. I thought a prefab would reference to the imported object but instead it saves the object again so that my game size will be doubled or tripled. Is there any other way of making prefabs of imported objects and why is the size of my prefab so high?