The comparison people usually get wrong
Most comparisons line the two up on thermal resistance per inch and stop there. That misses what actually goes wrong in a Houston house.
Fiberglass slows heat moving through it. It does not stop air moving around it. In a house with an unsealed ceiling plane — top plates, can lights, flue chases, an uninsulated attic hatch — hot humid air moves straight past the insulation, and adding more of it changes less than you would expect.
Spray foam seals and insulates in the same pass. That is the real difference, and it is why the answer here is so often foam even though fiberglass is cheaper per square foot.
That said: fiberglass is genuinely the better buy in some situations, and we will say so when it is. The same is true of blown-in on an attic floor.
Compare
Side by side
| Fiberglass / blown-in | Spray foam | |
|---|---|---|
| Slows heat | Yes | Yes |
| Stops airflow | No | Yes |
| Fills irregular cavities | Has to be cut around obstructions | Expands into them |
| Settles over time | Some settlement is normal | Adhered, does not settle |
| Works in a closed wall | Yes, dense-packed through small holes | No, needs an open cavity |
| Ductwork in the attic | Ducts stay in the hot zone | Roofline application brings them inside |
| Cost per square foot | Lower | Higher |
| Best when | Ducts are not in the attic, or budget has to cover more area | Air leakage is the actual problem |
General material behavior, not a claim about a specific product or a specific house.
Detail
When we recommend fiberglass
It is a different product with a different job, and these are the cases where it wins.
- The ductwork is not in the atticThen there is much less to gain from sealing the roofline.
- The roof is near replacementDo not commit to an unvented assembly you may have to open up in two years.
- Finished wallsDense-pack goes in through small holes; foam cannot.
- Budget has to cover more areaCovering the whole attic in blown-in beats foaming a third of it.
Questions
Common questions
In a house where air leakage is the real problem — which in Houston is most of them, especially with ducts in the attic — usually yes. Where it is not, we will tell you, because selling you the expensive answer to the wrong problem is how you end up doing it twice.
Yes, and it is common. Foam where sealing matters, blown-in where depth is all you need. That is often the best value scope in a house.
A tighter house needs its ventilation designed rather than left to leaks. If your scope changes the envelope significantly we will raise it on site — it is a real consideration, and we treat it as one.
The visit is free. Someone comes out, looks at the building and gives you a written scope and a price, and the decision stays yours.
48 cities across the eight-county Houston–Galveston region — Harris, Fort Bend, Montgomery, Brazoria, Galveston, Chambers, Liberty and Waller — plus five extended project markets.
They solve different problems. Blown-in fiberglass or cellulose on the attic floor adds R-value and leaves the attic vented. Spray foam at the roofline insulates and air-seals, and brings the ducts and air handler inside the insulated space. If your ducts are in the attic, we will point you toward sealing the roofline: the Department of Energy's Building America guidance says the efficiency gain of an unvented attic will likely outweigh the larger insulated area when the HVAC is up there. If they are not, blown-in can be the better value. We install both, so we will tell you which one fits.
Get it looked at properly
One visit, a written scope, and a written price.
(832) 737-0787Greater Houston, plus extended project markets.