Overview
Interior doors are simpler than exterior ones. There is no weather to keep out, no security to worry about, no insulation duty, so I am not chasing R-values or weatherstripping here. But two decisions drive everything, and most people skip past both. The first is slab versus prehung: do you buy just the door panel, or the door already mounted in its own frame with the hinges and bore done? The second is the core: hollow-core, solid-core, or solid-wood. That choice sets the heft of the door, how much sound it blocks, and the price. After those two calls, you pick the operating style for the opening: a standard swing, a bifold, a bypass slider, a pocket door, or a barn door. Each one fits a different clearance situation. The way I think about it: match the door to the room, the opening, and whether you actually want sound control. A bedroom and a pantry have different jobs. Get the slab-versus-prehung call and the core right, and the rest is trim work. This guide pairs with our exterior-door-types and drywall-types-and-thickness references.
Slab vs Prehung
A slab is just the door panel, nothing else. You reuse the existing frame and hinges, which means you cut the hinge mortises to match, bore the holes for the knob and latch, and trim the slab to fit the opening. That takes more skill and a steadier hand, but it is cheaper and it is the right move when you are replacing a door in a jamb that is still square and solid. A prehung door comes already mounted in its own jamb, with the hinges installed and the knob bore done at the factory. You set the whole unit into the rough opening, shim it, plumb it, and fasten it. It is far easier to hang a door true this way because the factory already got the panel-to-frame relationship right. Prehung is the standard for new construction and any brand-new opening, but it costs more and you end up replacing the casing and trim around it. So the call is simple: use a slab for a straight swap into a good existing jamb, and go prehung for a new opening or when the old jamb has racked out of square. Hanging a slab true in a bad frame is a fight you will lose.
Hollow-Core vs Solid-Core vs Solid-Wood
The core is what you feel when you swing the door and what you hear through it. Hollow-core doors are a thin skin, usually molded hardboard, stretched over a cardboard honeycomb inside. They are light, cheap, and the builder-grade default in most tract homes. They also feel flimsy, block almost no sound, and dent if you bump them with a vacuum. Solid-core doors use that same kind of skin over a dense composite or MDF core. They are much heavier, they swing with authority, they feel solid when they latch, and they block sound well. This is the upgrade that makes a house feel actually built, and it is what I want on bedrooms, bathrooms, and offices where privacy matters. Solid-wood doors are the real thing: wood stiles and rails with wood or glass panels. They are premium and heavy, they carry the high-end and historic look, but real wood swells and moves with humidity, so they can stick in a damp season. For the money, solid-core is the single best bang-for-buck upgrade in the whole interior. You feel the difference the first time you close one.
Operating Styles
After the core, you pick how the door moves in the opening. The swing is the standard hinged door everyone knows. It seals well and feels normal, but it needs floor clearance for the arc, so it is a problem in tight rooms. A bifold folds into panels that hinge together, which is the classic closet door. It needs no floor track to trip on, but the panels are usually flimsy and the pivot hardware works loose over time. A bypass or sliding door is two panels that slide past each other on a track, again common for closets, but you can only ever open half the opening at once. A pocket door slides into a cavity built inside the wall, so it takes zero floor space and shines in a tight bathroom or a small laundry. The catch is the hardware hides inside the wall, so a repair means opening drywall. A barn door slides on an exposed track mounted on the wall above the opening. It saves floor space and looks sharp, but it does not seal and it does not soundproof, and it needs open wall space beside the opening for the door to park. Match the style to the clearance you have and to whether the opening actually needs to seal.
FAQ
Is a solid-core door worth the extra money? For bedrooms, bathrooms, and offices, yes. It is the cheapest upgrade that gives you real sound control and makes the door feel substantial instead of hollow. For a closet or a pantry where nobody cares about noise, hollow-core is fine and saves money.
Can I replace a hollow-core door with a slab, or do I need a prehung? If your existing jamb is square, plumb, and solid, buy a slab and reuse the frame. You will need to transfer the hinge mortises and bore the knob holes to match. If the jamb is racked, damaged, or you are widening the opening, go prehung and reset the whole unit.
Do barn doors give any privacy? No. A barn door rides outside the wall on an exposed track and does not seal against a stop, so sound and light leak around all four edges. Use them for pantries, closets, or rooms where privacy does not matter, not bathrooms.
What is the hardest door for a DIYer to hang? Hanging a slab true in an out-of-square jamb is the tough one, because you are fighting a frame that is already wrong. A prehung unit is far more forgiving since the factory set the panel in the frame, and you just shim it plumb in the rough opening.