Fiberglass vs Spray Foam Insulation: Pros, Cons, and Cost

Before spray foam insulation: bare, uninsulated attic roof deck in a Rio Grande Valley home

Both keep a Valley home comfortable. They work differently, cost differently, and shine in different places.

When it is time to insulate or upgrade your Rio Grande Valley home, two names come up again and again: fiberglass and spray foam. Both keep your home more comfortable and can lower your AEP Texas or Magic Valley Electric bill, but they work differently, cost different amounts, and shine in different situations. Choosing the right one comes down to your budget, your goals, and the specific part of your home you are insulating.

This guide compares fiberglass and spray foam head to head, with a clear table, honest pros and cons, cost estimates, and guidance on which to pick for your Valley home.

Key takeaways

Fiberglass is cheaper up front; spray foam performs better per inch.
Only spray foam air seals, and only closed-cell blocks moisture.
Fiberglass runs about $1.50 to $3.50 per sq ft blown in; foam about $1.50 to $4.50 per board foot.
Many Valley homes use both, matched to each part of the house.

The quick comparison

Use this as a starting point, then read on for the details that will help you decide.

Feature	Fiberglass	Spray Foam
R-value per inch	Batts about R-3 to R-4; blown-in about R-2.2 to R-2.7	Open-cell about R-3.5 to R-3.8; closed-cell about R-6 to R-7
Air sealing	No, air moves around it	Yes, forms a continuous air barrier
Moisture barrier	No	Closed-cell acts as a vapor and moisture barrier
Up-front cost	Lower	Higher
Adds structural strength	No	Closed-cell adds rigidity
Best for	Walls, floors, budget attic top-ups	Attics, air sealing, tight or moisture-prone spaces
Install	Batts by hand or blown-in loose-fill	Sprayed by trained professionals

Figures are typical ranges. Your real numbers depend on thickness and installation quality.

Fiberglass insulation: pros and cons

Fiberglass has been the go-to insulation for decades. It comes as batts (rolls that fit between studs and joists) and as blown-in loose-fill for attics. It is made from fine glass fibers that trap air and slow heat flow.

Budget-friendly. Fiberglass is one of the most affordable insulation options, which makes it easy to insulate a lot of space for less.
Widely available and proven. It is a well-understood product with a long track record.
Good for walls and top-ups. Batts provide about R-13 to R-21 in walls, and blown-in fiberglass is great for adding depth to a Valley attic.
Non-combustible. Glass fibers do not burn.
No air sealing. Fiberglass slows heat but does not stop air leakage, so hot, humid Valley air can still move around it.
Sensitive to moisture. If it gets wet, fiberglass loses effectiveness and can stay damp, which is a real risk in the humid RGV.
Performance depends on install. Gaps, compression, and voids reduce its real-world R-value, so careful installation matters.

Spray foam insulation: pros and cons

Spray foam is applied as a liquid that expands and hardens, filling gaps and cracks as it cures. It comes in two types: open-cell (lighter, cheaper, great air barrier) and closed-cell (denser, higher R-value, moisture barrier, adds structure).

Air sealing built in. Foam expands into gaps and forms a continuous air barrier, which stops the leaks that waste your AC dollars.
High R-value per inch. Closed-cell reaches about R-6 to R-7 per inch, so it performs well even in tight spaces.
Moisture control. Closed-cell foam acts as a vapor and moisture barrier, a real plus in the humid Valley climate.
Cooler attics. Sprayed on the roof deck, foam can bring the attic into your conditioned space and protect ductwork from the extreme RGV heat.
Long-lasting. Foam does not settle or sag the way loose materials can.
Higher up-front cost. Foam costs more than fiberglass to install.
Professional install required. It must be applied by trained crews with the right equipment.
Harder to remove later. Because it bonds to surfaces, foam is more involved to take out than batts.

How much do they cost?

Cost is one of the biggest factors, so here are rough estimates. Remember that a real quote depends on your home, the area being insulated, and the thickness required.

Fiberglass. Among the most affordable options. Blown-in attic insulation runs roughly $1.50 to $3.50 per square foot, and batts are typically lower still.
Spray foam. Runs roughly $1.50 to $4.50 per board foot, with closed-cell costing more than open-cell because it is denser and higher performing.

Spray foam costs more up front, but its air sealing and high R-value can lead to greater energy savings over time, especially in the Valley where the AC runs for the better part of the year. Think of it as a higher investment with a stronger performance payoff.

Which should you choose for your Valley home?

There is no single winner, because the best choice depends on where and why you are insulating.

Choose fiberglass. When you want strong performance on a budget, particularly for wall cavities, floors, and topping up an attic. Pair it with separate air sealing to close the performance gap.
Choose spray foam. When air sealing, moisture control, and maximum performance in a tight space matter most, or when you want a cooler, conditioned attic. The moisture barrier is a real advantage in the humid RGV.

Many Valley homes benefit from a mix. For example, closed-cell foam or careful air sealing where leaks are worst, plus cost-effective blown-in or batt insulation across larger areas. A professional can help you match materials to each part of your home and your budget.

Why the Valley changes the comparison

Ducts in a hot attic

Most Valley homes run ducts and the air handler through the attic. ENERGY STAR says about 20 to 30 percent of the air moving through a typical duct system is lost to leaks, holes and poor connections. In a hot attic that loss hurts.

Air leaks and humidity

Damp air pulled in through leaks adds moisture the AC has to remove. Fiberglass does not stop that air. Foam, or separate air sealing, does.

Slab foundations

Most homes here sit on a slab, so there is no crawl space to treat. The attic is where both options compete.

A long cooling season

The AC runs most of the year, so improvements that keep heat and damp air out have many months to pay back.

Strong sun on the roof

A fiberglass attic paired with a radiant barrier on the rafters cuts roof heat at a lower price than foam.

Roof leaks

Foam on the roof deck can hide a slow leak. Any leak needs to be fixed before foam goes on.

Pick the tool for the job

Fiberglass wins when

The attic is dry and open
You only need more depth
Ducts are sealed and in fair shape
Walls are open during a remodel
Budget is the main concern
It is a rental or a house you may sell soon

Spray foam wins when

Ducts run through a very hot attic
Rooms stay hot no matter the setting
The house leaks a lot of air
Bonus rooms over the garage never cool
It is a metal shop or warehouse
You plan to stay for years

Frequently asked questions

Is spray foam better than fiberglass?

Spray foam performs better in air sealing, R-value per inch, and moisture control, but it costs more. Fiberglass is more affordable and works well for walls and attic top-ups. The best choice depends on your goals and budget.

Which is cheaper, fiberglass or spray foam?

Fiberglass is cheaper up front. Spray foam costs more to install but can deliver greater energy savings over time thanks to its air sealing, which matters during the long Valley cooling season.

Can I use both in the same home?

Absolutely. Many Valley homes use spray foam or air sealing where leaks are worst and fiberglass or blown-in across larger areas to balance performance and cost.

Does fiberglass or spray foam handle Valley humidity better?

Closed-cell spray foam acts as a moisture barrier, giving it an edge in the humid RGV. Fiberglass is more sensitive to moisture and should be kept dry.