Before we can answer that, let’s look at the evidence.
Gravity: it is a pervasive but weak force. It is the weakest of all the forces of physics but its effect accumulates. When enough of it accumulates it becomes extremely powerful. Black holes result when a large amount of matter gets concentrated. The gravity in a black hole is so powerful that even light is drawn into it.
But in heaven gravity behaves differently. Richard Sigmund saw children playing a game where one child hovers in the air above a circle of children who gleefully push the hovering child back and forth across the circle. He also saw children jump out of trees and float to the ground like cotton balls without any harm. Once he rose up defying gravity and the farther up he went the more distant villages he could see and hear. Yet people can walk on the street or grass as if being held down by gravity. In heaven there appears to be some gravity, but it behaves differently from the gravity we know on Earth.
Second Law of Thermodynamics: Several people report that leaves never die, flowers never fade, and blades of grass are always green. Nothing dies in heaven, not people, not animals, not plants, not tree limbs, not flowers, not grass. The fruit on the trees never spoils; nothing rots and decomposes. On Earth, the molecules from which all living matter is made eventually break down. All energy moves from a region of high concentration to a homogeneous dispersion. Nothing lives forever here; all life molecules eventually break down. The complex molecules of life break down into smaller more permanent molecules such as water and carbon dioxide.
Water: Several people were able to be in the waters of heaven, the River of Life, the lake, the sea. When they came out of the water they were not wet and their hair was perfectly dry. Furthermore, after being in the water of the River of Life, something about them had changed. Some of the results of their Earth life had been washed away. This includes all memories of the effects of sin, so they were ready for their heavenly life. (I guess when they came back here all those benefits were nullified until they go back permanently.) Another person saw two different waters flowing under the throne and the two waters never intermingled. Clearly water is different there; it not like the H2O of Earth. Here the water molecules cling to your skin, clothes, and hair until they evaporate into the air. They do not have the healing effect that the waters of heaven have.
Light: There is no sun or moon or stars in heaven. But everything is in brilliant light, brighter than any light on Earth. The light is the glory of God radiated throughout heaven. The glory of God powers everything, including, as one person reported, the creation of various foods that we will eat beyond the fruit of the Trees of Life along the River of Life. It is always light in heaven; there is no night. So sleep is never needed. But we will never get tired and need rest like we do here. I enjoy naps, more so as I get older, but there I will always enjoy what I am doing and never tire.
Buildings: Everything constructed in heaven fits perfectly together. No nails, mortar or other fasteners are required. The closest we come to that on Earth is some of the Roman and Egyptian structures made of stone. Everything else here requires some fasteners to hold it together. Apparently this is not so in heaven.
Bodily Functions: One physician, Richard Eby, studied his heavenly body and saw that it was translucent. He could see through it to the flowers beneath and behind him. He also saw that he had no internal organs, no alimentary canal. As a result whatever we eat just evaporates after we eat it and there is no bodily waste. As a result, there are no bathrooms there. Also we never get dirty and need a shower or bath.
Putting all this together, I conclude heaven is not made with atoms and molecules like this Universe is. One eyewitness said the same thing. He didn’t know what the substance of heaven is, and neither do I. Perhaps we can’t know until we get there and can do heavenly science. The laws of physics that we know for this Universe also do not seem to apply there. Not only are the substances of heaven different from this world, the laws that govern everything there are different from those here. As a scientist, it will be exciting to explore all of these questions when we are there. Then maybe we will be able to answer the question, “What is heaven made of?”