Crawl Space Insulation: 5 Types Compared for 2026

By the Crawl Space Saver editorial team · Updated October 28, 2026

Crawl space insulation keeps floors warmer and can lower heating and cooling costs, but the wrong choice in a damp space fails quickly. Moisture decides most of it. Here are five common types, where each one goes and how to choose.

First, decide where to insulate

There are two approaches. In a vented crawl space, insulation goes between the floor joists above, so the crawl space stays outside the home’s thermal boundary. In a sealed, conditioned crawl space, insulation goes on the foundation walls, and the floor above is usually left alone. ENERGY STAR links to guides on both from its page on sealing and insulating crawl spaces, and warns that sealing a home can cause combustion appliances to backdraft.

5 types of crawl space insulation

1. Fiberglass batts. Cheap and familiar, but they absorb moisture, sag and lose performance in damp spaces. Many pros avoid them in humid crawl spaces unless the space is sealed and dry.

2. Rigid foam board. Foam board resists moisture and works well on walls, with taped seams for air sealing. It can be a good fit for sealed crawl spaces. Check local code for fire-protection and termite rules.

3. Closed-cell spray foam. It insulates, air seals and resists moisture, but it costs more. It suits walls and rim joists in many jobs. It must be installed by qualified applicators.

4. Open-cell spray foam. It is less moisture-resistant, so it is generally not preferred in crawl spaces where humidity is a concern. Ask your installer why they choose it if offered.

5. Mineral wool. It repels water better than fiberglass and resists fire, and some builders use it between joists or on walls. Cost is moderate.

How much insulation do you need?

The recommended R-value depends on your climate zone and where you install it. Recommended R-values vary by climate zone, and local code sets minimums. Do not take a flat number from a salesperson. Confirm the target for your state.

Moisture comes first

Insulation cannot fix a wet crawl space. Damp batts hold water against the wood and can speed rot and mold. Controlling the ground and air with a vapor barrier, sealed vents and a dehumidifier is the foundation, which is why insulation is often an add-on to full encapsulation. Read about crawl space humidity to see why.

Common mistakes

Installing fiberglass over a wet crawl space, leaving gaps that let air through, covering a leaking pipe, blocking required combustion air and mixing floor and wall insulation without a plan all cause trouble. Ask any installer to explain their moisture and air-sealing plan before insulation.

What it costs

Cost depends on material, area and access. Spray foam typically costs more than batts, with foam board in between. Because pricing varies widely, get written quotes and compare R-values and warranties. Our cost guide shows how insulation fits into an overall encapsulation quote.

Seasonal timing

People call about insulation in cold months, when the floors get cold. But the right time to fix moisture and insulate is whenever you can get a pro out there. Waiting through another damp summer usually makes it worse.

Frequently asked questions

Crawl Space Saver is a free referral service. We are not a contractor. We connect homeowners with independent local crawl space professionals, who set their own prices and do the work.