Knock on almost any interior wall in a modern American home and you are tapping on drywall, yet most people have no idea what is in drywall. At its core, drywall is a panel of gypsum sandwiched between two layers of paper. That simple recipe, refined with a few additives, makes the lightweight, fire-resistant boards that line nearly every room built since the mid-twentieth century. Understanding what goes into it helps you choose the right type, handle it safely, and know when an old wall might hide hazards.
The Gypsum Core
The heart of every drywall panel is gypsum, a soft mineral known chemically as calcium sulfate dihydrate. Manufacturers grind raw or synthetic gypsum, heat it to remove most of its water, then rehydrate it into a paste that is pressed into flat sheets and dried. The result is a rigid, fire-resistant core.
Gypsum is naturally flame-resistant because it contains chemically bound water. When exposed to fire, that water releases slowly as steam, which is why drywall buys precious time during a house fire. This property is the main reason building codes require it.
The Paper Facing
Two layers of paper wrap the gypsum core, one on the front and one on the back. The face paper is smooth and ready to accept paint or texture, while the back paper provides structural backing. Recycled paper is common in this layer, making drywall one of the more sustainable building products.
Some specialty boards swap paper for fiberglass mat facing, which resists mold and moisture far better than paper. These are common in bathrooms and basements.
Additives in the Mix
Beyond gypsum and paper, manufacturers blend in small amounts of other materials to give boards specific properties:
- Starch to bond the paper to the core
- Fiberglass for added fire resistance in Type X panels
- Foaming agents to create tiny air pockets that reduce weight
- Vermiculite or clay in fire-rated boards
- Silicone or wax in moisture-resistant “green board”
- Boric acid as a fungicide and to improve fire performance
These additives are what separate a basic panel from a fire-rated, moisture-resistant, or soundproofing board.
Common Types of Drywall
Not all drywall is the same. The major types you will encounter include:
- Standard (1/2 inch): The everyday choice for walls and ceilings
- Type X (5/8 inch): Fire-rated board with added glass fibers for garages and shared walls
- Moisture-resistant (green board): Treated for damp areas like bathrooms
- Mold-resistant: Often with fiberglass facing and treated core
- Soundproofing: Denser panels, sometimes with a damping layer, to block noise
Joint Compound and Tape
The panels themselves are only part of a finished wall. To join sheets seamlessly, installers apply paper or fiberglass mesh tape over the seams, then coat them with joint compound, sometimes called mud. This compound is largely gypsum and limestone with water and additives, sanded smooth once it dries. The combination of board, tape, and compound creates the flat, paintable surface you see.
Legacy Hazards in Old Drywall
Here is where homeowners need to be careful. Drywall and its related products made before the late 1970s can contain hazardous materials.
Asbestos was sometimes added to joint compound and occasionally to the boards themselves for fire resistance, especially in homes built or remodeled before 1980. Disturbing asbestos-containing material releases fibers that are dangerous to inhale.
Lead may be present in paint applied over old drywall, and sanding or demolition can release lead dust.
If your home was built before about 1980 and you plan to cut, sand, or remove walls, test the materials first. Hire a certified inspector to take samples, and use a licensed abatement professional if asbestos or lead is confirmed. Never dry-sand or demolish suspect material without testing.
Working With Drywall Safely
Even modern drywall produces fine gypsum and silica dust when cut or sanded. Protect yourself by:
- Wearing an N95 or better respirator
- Using a dust mask and eye protection
- Cutting with a utility knife and snapping rather than sawing when possible
- Using a wet-sanding sponge or vacuum sander to control dust
- Ventilating the work area
How Drywall Is Made
Knowing how drywall is manufactured explains a lot about its properties. Raw gypsum rock or synthetic gypsum recovered from power plants is crushed and heated in a process called calcining, which drives off most of the water and creates a powder. That powder is mixed with water and additives into a wet slurry, then sandwiched between two continuous sheets of paper as it moves down a production line. The board is cut to length, dried in a long oven to remove the remaining moisture, and trimmed to standard sizes like 4 by 8 feet. This efficient process is why drywall is so affordable and widely available compared to the labor-intensive plaster it replaced.
How Drywall Compares to Plaster
Before drywall became standard in the mid-twentieth century, interior walls were built with lath and plaster, a labor-intensive system of wooden strips coated in wet plaster. Drywall replaced it because panels install in a fraction of the time and require less skilled labor. If you own an older home, you may have plaster walls, which are denser and harder than drywall but more prone to cracking and harder to patch.
You can tell the difference by pressing a thumbtack into the wall: it pushes easily into drywall but resists hard plaster. This matters when hanging shelves or art, since each requires different anchors.
Choosing the Right Board for Each Room
Matching the board to the location prevents problems down the road:
- Use standard 1/2-inch board for most bedroom and living-area walls
- Use moisture-resistant or mold-resistant board in bathrooms and laundry rooms
- Use Type X fire-rated board where code requires it, such as garages and walls shared with living space
- Use cement board, not drywall, directly behind tile in showers
Picking correctly the first time saves you from tearing out failed walls later.
The Bottom Line
Drywall is a deceptively simple product: a fire-resistant gypsum core wrapped in paper, fine-tuned with additives for strength, moisture resistance, and fire ratings. Knowing its composition helps you pick the right board for each room and handle it safely. The most important takeaway is to treat any pre-1980 wall with caution and test for asbestos and lead before you disturb it, protecting your health while you renovate.
