Is Spray Foam Really Better Than Fiberglass?

Let's be honest—you've probably heard conflicting advice about insulation. Your contractor says one thing, your neighbor swears by another, and Google gives you a thousand different opinions. So what's the real story with spray foam vs. fiberglass?

After 16+ years of insulating homes across the DC metro area, we've seen it all. We've retrofitted homes with failing fiberglass, and we've watched spray foam transform uncomfortable houses into energy-efficient sanctuaries. Here's what we've learned.

The Problem Most DC Homeowners Don't Know They Have

Walk into most homes built in the last 30 years around DC, and you'll find fiberglass insulation. It's pink, it's fluffy, and it looks like it's doing its job. But here's what most homeowners don't realize:

Fiberglass only works if air doesn't move through it.

Think of fiberglass like a winter sweater. It keeps you warm by trapping still air. But what happens when the wind blows through that sweater? You get cold fast. The same thing happens in your walls.

In our humid DC climate, air is constantly moving through your walls, carrying moisture and energy with it. Fiberglass can't stop this air movement—it can only slow it down.

Why Spray Foam Changes Everything

Spray foam doesn't just insulate—it seals. When we spray foam into your walls, it expands to fill every crack, gap, and crevice. It creates an airtight barrier that stops air movement completely.

Here's what that means for your home:

1. Your Energy Bills Actually Drop

We regularly see 30-50% reductions in energy costs after spray foam installation. Why? Because your HVAC system isn't working overtime to replace the conditioned air that's leaking out through gaps in fiberglass insulation.

2. No More Hot and Cold Spots

You know that bedroom that's always too hot in summer and freezing in winter? That's usually an air sealing problem, not an insulation problem. Spray foam solves both.

3. Better Indoor Air Quality

When outside air can't sneak into your home through wall cavities, you're not bringing in pollen, dust, and humidity. Your indoor air stays cleaner and more comfortable.

But What About the Cost?

Yes, spray foam costs more upfront than fiberglass. We're not going to sugarcoat that. But here's what we tell every homeowner:

Fiberglass is cheap to install but expensive to live with.

When you factor in the energy savings, improved comfort, and the fact that spray foam lasts for the life of your home (while fiberglass may need replacement), the math usually works out in spray foam's favor.

The Numbers Don't Lie

Let's talk R-values (that's the measure of insulation effectiveness):

• Closed-cell spray foam: R-6.5 to R-7 per inch
• Open-cell spray foam: R-3.5 to R-4 per inch
• Fiberglass batts: R-2.2 to R-4 per inch

But here's the kicker—those R-values for fiberglass assume perfect installation with no air movement. In the real world, air leaks can reduce fiberglass effectiveness by 50% or more.

What About Moisture?

In DC's humid climate, moisture is a big concern. Fiberglass absorbs moisture like a sponge, which reduces its insulating ability and can lead to mold growth.

Closed-cell spray foam, on the other hand, acts as a vapor barrier. It doesn't absorb moisture, and it prevents humid air from reaching the wood framing in your walls.

The Bottom Line

Is spray foam better than fiberglass? For most DC-area homes, absolutely. But it's not just about the insulation—it's about creating a complete building envelope that controls air movement, moisture, and energy loss.

That said, spray foam isn't right for every situation. If you're on a tight budget and your home already has good air sealing, fiberglass might be adequate. But if you want maximum comfort, energy savings, and long-term performance, spray foam is the clear winner.