Why is the concept of density related to floating and sinking? Is there any object which will neither sink nor float?

• The positioning of molecules affects the density of an object. 
• Objects with tightly packed molecules are denser than those where the molecules are spread out.
• Objects that are denser than water sink and those less dense float.
• Hollow things often float too as air is less dense than water.      
• Objects that neither float nor sink but flink is not present naturally on Earth. But one can prepare such an object by using a variety of materials and combining them in a way that it flinks.