If you’re planning to insulate your home, you’ve probably come across the debate: spray foam insulation vs fiberglass. One’s the old reliable choice you’ve seen for decades, and the other’s the modern system promising better efficiency and comfort. But when you strip away the marketing, which one actually performs better, and which is the best insulation for homes long term?
The truth is, both insulation types serve a purpose. Fiberglass is inexpensive and widely available, but it leaves small air gaps that allow drafts, moisture, and allergens to sneak through. Spray foam, on the other hand, creates an airtight seal that locks in comfort, lowers energy bills, and keeps humidity at bay. The difference is like closing your door versus just pulling it almost shut.
In this guide, we’ll break down the real-world differences between spray foam and fiberglass insulation from performance and cost to environmental impact, so you can make the right decision for your home. Whether you’re building new, remodeling, or simply tired of high utility bills, you’ll walk away with the clarity you need to invest wisely.
At IPS, we believe homeowners deserve insulation systems that perform as promised. Our Therma-Lok® open-cell and Therma-Shield® closed-cell spray foams are engineered for efficiency, comfort, and confidence, because your home deserves better than “good enough.”
QUICK COMPARISON: SPRAY FOAM INSULATION VS FIBERGLASS
| Feature | Spray Foam Insulation | Fiberglass Insulation |
|---|---|---|
| Air Seal | Excellent – completely seals gaps and cracks | Poor – allows air movement through gaps |
| R-Value per Inch | 4.1 (open-cell) / 7.1 (closed-cell) | 3.1–3.4 (no air seal, think of a cooler with the lid cracked) |
| Moisture Resistance | High – resists moisture and mold growth | Low – can trap moisture and support mold |
| Longevity | 25+ years with minimal degradation | 10–20 years before sagging or settling |
| Energy Efficiency | Superior – prevents heat loss and drafts | Moderate – relies solely on R-value |
| Cost | Higher upfront, lower lifetime cost | Lower upfront, higher long-term cost |
An important note about R-Value…
R-Value reflects how well insulation restricts heat transfer. However, the R-Value rating of an insulation system is only as effective as it’s airseal. Think about a cooler with the lid cracked. Most coolers have fantastic R-Value and are extremely insulated. However, if the lid is cracked or in other words is not sealed, the R-Value of the cooler is rendered virtually useless because there is air coming in through the cracked lid. Same with fiberglass and other insulation systems. There is no air seal, which means the R-Value of that system is being negated by air seeping in through every crack and crevice.
What Is Spray Foam Insulation (and Why It Outperforms Fiberglass)?
Spray foam insulation is a two-part liquid system that expands on contact to create a seamless, airtight barrier. Unlike traditional insulation that simply fills space, spray foam adheres directly to surfaces sealing every crack, gap, and joint. The result is a continuous layer of protection that locks in comfort and locks out the elements.
There are two main types of spray foam insulation: open-cell and closed-cell.
- Open-cell foam, like Therma-Lok®, is soft, flexible, and ideal for interior walls, attics, and ceilings. It provides excellent sound absorption and expands dramatically to fill even the tightest spaces.
- Closed-cell foam, such as Therma-Shield®, is dense, rigid, and moisture-resistant making it perfect for exterior walls, crawlspaces, pole barns and basements where strength and vapor control matter most.
Both types share one thing in common: they deliver insulation and air sealing in a single step. By reducing air permeance the main source of energy loss in most homes, spray foam can dramatically lower heating and cooling costs while improving overall comfort and indoor air quality.
At IPS, our spray foam systems are engineered for consistency and performance. Every batch of Therma-Lok® and Therma-Shield® is tested to ensure even spray patterns, strong adhesion, and reliable yield, so you can rest easy knowing your home is insulated for the long haul.
What Is Fiberglass Insulation (and How DOES It Compare to Spray Foam)?
Fiberglass insulation is known as the classic, budget choice for home insulation. It’s made from fine glass fibers bound together into batts or blown-in material that trap pockets of air creating a thermal barrier between indoor and outdoor temperatures. Because of its affordability, and availability, fiberglass has been one of the most commonly used insulation materials.
Fiberglass is a good fit for homeowners who want a budget-friendly option up front. It’s commonly installed in attics, walls, crawlspaces, and floors, and can be easily fitted between framing or blown into open cavities. When installed correctly and kept dry, fiberglass can provide years of dependable performance with minimal maintenance.
However, fiberglass works best when combined with proper air sealing. On its own, it doesn’t stop airflow through gaps and cracks, which can lead to drafts and uneven temperatures. It can also lose some effectiveness over time as it settles or compresses, and in humid environments, moisture control becomes especially important.
In short, fiberglass insulation is a practical choice for many homes. It’s a good fit for renovations, short-term projects, or situations where upfront cost efficiency is the top priority. For homeowners looking to take energy efficiency a step further, pairing fiberglass with modern air sealing or upgrading to spray foam can create a more complete and high-performance system.
Spray Foam vs Fiberglass: Performance Breakdown
When it comes to insulation, performance isn’t just about R-value, it’s about how your home actually feels and performs day to day. Let’s break down the key areas where spray foam and fiberglass differ in real-world application.
A. Energy Efficiency
Both fiberglass and spray foam insulate your home, but they do it in very different ways.
Fiberglass relies on trapping air between glass fibers to slow heat transfer, while spray foam creates an airtight seal that stops air movement entirely. That means less conditioned air leaking out and fewer drafts sneaking in.
- Spray Foam: Delivers superior real-world efficiency, often cutting heating and cooling costs by up to 50%.
- Fiberglass: Provides reliable thermal performance but depends heavily on precise installation and complementary air sealing to reach full efficiency.
B. Comfort and Air Quality
Comfort is about more than temperature, it’s about consistency.
Because spray foam forms a complete air barrier, rooms maintain a more even temperature year-round and resist outdoor humidity. It also keeps out pollen, dust, and outdoor allergens.
- Spray Foam: Keeps temperatures steady and air cleaner.
- Fiberglass: Performs well in moderate climates but can allow air movement and minor drafts, especially around seams or penetrations.
C. Moisture and Mold Resistance
Moisture is insulation’s worst enemy.
Closed-cell spray foam, like Therma-Shield®, provides a built-in moisture barrier that protects against leaks and condensation. Fiberglass, while not absorbent itself, can trap moisture if water seeps into wall cavities, increasing the risk of mold over time.
- Spray Foam: Excellent moisture resistance and structural rigidity.
- Fiberglass: Works best in dry, ventilated spaces or when paired with a separate vapor barrier.
D. Longevity and Maintenance
Once installed, spray foam insulation is set it and forget it. It doesn’t settle, shift, or deteriorate over time. Fiberglass, however, can compress or sag, especially in vertical walls or high-humidity areas.
- Spray Foam: Lasts 25+ years with virtually no degradation.
- Fiberglass: Typically lasts 10–20 years before loss of effectiveness.
E. Cost and Return on Investment
There’s no denying that fiberglass costs less upfront. But when you account for energy savings, comfort, and longevity, spray foam overwhelmingly pays for itself over time.
- Spray Foam: Higher upfront cost, lower lifetime cost.
- Fiberglass: Lower upfront cost, but higher long-term energy use and potential for reinstallation.
QUICK TAKE AWAY
Spray foam insulation provides a tighter air seal, higher R-value per inch, and better moisture resistance while fiberglass remains the cost-effective classic for quick installs.
Spray Foam vs Fiberglass: Environmental Impact
As building science evolves, sustainability has become just as important as performance, and insulation plays a major role in a home’s overall environmental impact.
Fiberglass insulation has long been seen as a sustainable choice due to its high recycled content and relatively low chemical output. Many fiberglass products contain up to 60% recycled glass and sand, and they don’t off-gas once installed. It’s a tried-and-true option that helps homeowners meet green building standards at a low cost.
Spray foam insulation, however, has come a long way in recent years. Older foams used blowing agents with high Global Warming Potential (GWP), but today’s advanced systems, like Therma-Lok® and Therma-Shield® from IPS, use next-generation HFO blowing agents that dramatically reduce environmental impact. These energy efficient insulation systems offer low-GWP, zero-ozone-depleting chemistry while delivering superior insulation performance, meaning homes require less energy for heating and cooling over time.
In other words, spray foam doesn’t just insulate better, it helps your home consume less energy, lowering your carbon footprint year after year. When properly installed and maintained, the energy savings from spray foam can offset its environmental production footprint many times over.
So while fiberglass continues to be a sustainable mainstay in the market, modern spray foam systems have closed the gap, offering a balance of high performance and responsible chemistry. At IPS, that balance is the goal, helping homeowners insulate smarter, live more efficiently, and build for the future with confidence.
Final Verdict: Spray Foam vs Fiberglass
Both spray foam and fiberglass insulation can make a home more comfortable and efficient. The right choice simply depends on your priorities.
If you’re looking for a budget-friendly, familiar material that delivers dependable performance, fiberglass remains a proven option. It’s widely available, easy to install, and well-suited for short-term projects or renovations where cost is the main concern.
But if you’re after maximum comfort, long-term energy savings, and peace of mind, spray foam stands apart. By creating an airtight seal that keeps your conditioned air where it belongs, it turns your home into a more stable, efficient environment season after season.
At IPS, our high-performance systems, Therma-Lok® open-cell and Therma-Shield® closed-cell are engineered for to be the best insulation for homes. Every batch is tested for quality, ensuring contractors and homeowners alike can spray with confidence knowing their insulation is built to perform for decades.
LET’S TALK
Whether you have more questions, or you’re ready to spray foam your next project, give us call we’re happy to help. Innovative Polymer Systems (IPS) connects homeowners with certified contractors trained to install the nation’s leading spray foam systems. Whether you’re building new or upgrading an existing home, we’ll help you choose the right foam for your goals, and make sure it’s done right the first time.
Contact us today to get started, or to find a contractor near you.
