What Goes Under a Mattress? A Practical Guide to Bed Support & Protection

If you’re wondering “What goes under a mattress?”, you’re really asking how to support it properly so it stays comfortable, safe, and long‑lasting. The right base can affect how your mattress feels, how long it lasts, and even how clean it stays.

This FAQ-style guide walks through the most common options, what they do, and what to avoid.

Why Does What Goes Under a Mattress Matter?

A mattress needs even, stable support. The surface underneath:

Helps keep the mattress from sagging
Allows for airflow, which can reduce excess moisture buildup
Can raise the mattress to a more comfortable height
May be required to keep a warranty valid

Choosing the wrong base (or no base at all) can lead to premature wear, uneven feel, and potential safety issues.

What Are the Main Types of Mattress Support?

1. Box Spring or Foundation

A box spring (or modern solid foundation) is a supportive layer that usually sits between the mattress and bed frame.

Traditional box springs: Have a wooden frame with springs or flexible supports inside. These are commonly used with older innerspring mattresses.
Foundations: Often use wood or metal slats with a rigid top, designed to give firm, flat support (frequently used with foam or hybrid mattresses).

Many people choose a box spring or foundation because it:

Raises the mattress
Provides consistent support
Helps distribute weight across the frame

2. Platform Bed

A platform bed combines the frame and support surface in one piece. It usually has:

Closely spaced slats, or
A solid surface with ventilation holes

Platform beds can remove the need for a separate box spring, as long as the slats are not too far apart and are strong enough to hold the mattress and sleepers evenly.

3. Slatted Base

A slatted base uses wooden or metal slats laid across a bed frame.

Key points:

Slats should be flat, sturdy, and evenly spaced
Excessively wide gaps can lead to sagging areas in the mattress over time
Some designs include slightly flexible slats for a bit of extra give

Many foam and hybrid mattresses work well on firm, closely spaced slats.

4. Adjustable Base

An adjustable base lets you raise or lower the head and/or foot of the bed.

Designed to move with the mattress
Works mainly with flexible mattress types (such as many foam or hybrid models)
Should still provide solid, even support across the mattress surface

If using an adjustable base, make sure your mattress type is compatible with bending and movement.

Can You Put a Mattress Directly on the Floor?

Many people ask whether the answer to “What goes under a mattress?” can simply be “nothing but the floor.”

You can place a mattress directly on the floor, but there are trade-offs:

Potential benefits:

Very stable, firm surface
No need for a frame or foundation

Potential drawbacks:

Limited airflow, which may trap moisture against the underside
Mattress can be more exposed to dust, dirt, and pests
Heavier to lift, flip, or clean around
Some warranties may discourage floor use

If you choose floor placement, lifting the mattress regularly and allowing air to circulate around it can help keep it fresher.

Do You Need Anything Between the Mattress and the Base?

Sometimes, what goes under a mattress also includes protective layers.

Mattress Protector or Encasement

A mattress protector usually goes directly on the mattress (under the sheets), not under the base. However, some people use additional protection between a mattress and a rough or slatted base, such as:

A thin, breathable non-slip mat
A bunkie board (thin, rigid platform) for extra support over slats

These additions can:

Prevent the mattress from sliding
Smooth out uneven slats
Add a layer of separation between the mattress and frame

Bunkie Board

A bunkie board is a thin, solid panel designed to create a flat, supportive surface under a mattress, especially on slatted or metal frames.

It’s commonly used when:

Slats are too far apart
Extra support is desired for a foam or hybrid mattress

What Should You Not Put Under a Mattress?

Some surfaces can cause issues over time:

Very widely spaced slats that let parts of the mattress dip through
Old, broken, or sagging box springs that no longer support evenly
Non-breathable plastic sheets directly against the underside, which may trap moisture
Improvised supports (like stacked boxes or unstable objects) that can shift or collapse

If the base is unstable, uneven, or traps moisture, it is not a good long-term solution.

How Do You Choose the Right Support?

When deciding what goes under a mattress, consider:

Mattress type: Foam and hybrid mattresses often do best on firm, flat, well-supported surfaces; some traditional springs are designed with box springs in mind.
Slat spacing: Closer, sturdier slats offer more even support.
Height preference: Higher setups use both a frame and foundation; lower setups might use a platform bed or floor (with the trade-offs in mind).
Room conditions: In damp or humid spaces, airflow under the mattress becomes more important.

Whenever possible, matching the support type to the needs of your specific mattress design helps maintain its feel and structure over time.

✔️ Quick Mattress Takeaways

Key points consumers should understand about What Goes Under a Mattress

Even, stable support under your mattress helps reduce sagging and wear.
Box springs/foundations, platform beds, and slatted bases are the most common options.
Slat spacing and sturdiness matter, especially for foam and hybrid mattresses.
A bunkie board or non-slip layer can improve support over slats or metal frames.
Putting a mattress directly on the floor is possible but reduces airflow and can increase exposure to dust and moisture.
Avoid broken, sagging, or improvised supports that don’t provide a flat, stable surface.

With a clear understanding of what goes under a mattress, you can choose a setup that supports both your mattress and your comfort over the long term.