Search for the best insulation and you will find answers written for Minnesota. The Gulf Coast asks a different question of a building, so the ranking is different here. This is an honest comparison of the three materials we get asked about most, judged against what a Houston house actually faces.
What Houston specifically demands
Three conditions decide the answer here:
- A long cooling season and a short mild heating season, so the heat flow runs inward for most of the year.
- High dew points for months at a time, meaning moisture is pushing inward toward your cooled interior, not outward.
- Ductwork in the attic in the majority of homes, which turns attic temperature into a direct operating cost.
Insulation advice written for a heating climate frequently gets the vapor control backwards for this region, which is how walls rot in houses that never leaked.
Spray foam
Closed cell runs about R-6.5 per inch, cures rigid, blocks air and vapor, holds no water and adds stiffness to the assembly. Open cell runs about R-3.7 per inch, cures soft, absorbs sound well, stays vapor permeable and costs considerably less per square foot.
Strengths here. Foam is the only one of the three that is an air barrier as well as an insulator, which in this climate is the decisive property. It also does not settle, sag or lose performance over time, and closed cell is unaffected by water.
Limitations. Highest cost per square foot. Requires a trained crew and correct application in controlled lifts. Needs a thermal or ignition barrier over it to satisfy code.
Best for. Attic roof decks, exterior walls, metal buildings, crawl spaces, rim joists and anywhere moisture is in play. Details on closed cell and open cell.
Fiberglass
Spun glass fiber, as batt or blown loose fill, working by trapping still air. Roughly R-3.0 to R-3.8 per inch depending on product and installation.
Strengths here. By far the lowest cost per unit of R value. Widely available, quick to install, and genuinely effective in an assembly that is already air sealed and stays dry. It also does not burn.
Limitations. It is a filter, not an air barrier, so air moves through it freely. Wet fiberglass loses loft permanently. Its real world performance depends heavily on installation quality, and most of what we find underperforming was badly installed rather than badly made.
Best for. Attic floors over a properly sealed ceiling, especially where ducts are not in the attic. Interior walls for sound. Budget constrained projects. See fiberglass insulation.
Cellulose
Recycled paper fiber treated with fire retardant, blown dense packed or loose fill. Around R-3.2 to R-3.8 per inch.
Strengths. Good coverage around obstructions, high recycled content, and dense pack resists air movement better than loose fiberglass.
Limitations in this climate. This is where Houston changes the ranking. Cellulose is hygroscopic, meaning it absorbs and holds moisture from the air around it. In a region with months of high dew points, and in attics that see occasional roof leaks and storm intrusion, that is a meaningful liability. Wet cellulose compacts into a dense mat, holds water against the framing, loses R value and can support mold growth. It also settles over time, so the depth installed is not the depth you have in ten years.
Best for. Drier climates, and dense pack applications in walls where moisture is well controlled. We do not generally recommend it for Houston attics.
Side by side for a Houston home
- R per inch: closed cell foam, then cellulose and fiberglass roughly level, then open cell foam.
- Air sealing: foam clearly first, dense pack cellulose second, fiberglass last.
- Moisture tolerance: closed cell foam first, fiberglass second, cellulose last.
- Cost per square foot: fiberglass lowest, cellulose next, open cell, then closed cell highest.
- Longevity without maintenance: foam first, fiberglass second, cellulose last because of settling.
- Sound absorption: open cell foam first, cellulose second, fiberglass batt third.
So what should you actually buy?
If your ducts run through the attic, which is most Houston homes, foam at the roof deck is the highest value work available to you. Open cell across the deck, closed cell where moisture or shallow cavities are involved.
If your ducts are in conditioned space and the ceiling is intact, air sealing the ceiling plane and blowing fiberglass to depth gets you most of the benefit for a fraction of the price. That is an honest recommendation, and we make it regularly.
If you have a metal building, closed cell against the panel is the only answer that also solves condensation. See commercial insulation.
The most common outcome we specify is a mix: the expensive material only where nothing else will do, and the economical material everywhere it performs perfectly well.
Frequently asked questions
Is cellulose ever the right choice in Houston?
In dense pack wall applications with good moisture control it performs. For attics in this climate we would steer you elsewhere, mostly because of moisture absorption and settling.
Can I mix materials in one house?
Yes, and it is usually the best value specification. Foam where moisture and shallow cavities demand it, fiberglass where conditions are dry and depth is cheap.
Does higher R value always mean better?
No. R value measures resistance to conduction only. It says nothing about air movement, which in this climate is often the larger loss. That is why a lower R product that seals can outperform a higher R product that does not.
What about radiant barriers?
They address radiant gain and can supplement insulation. They are not insulation and do not seal air, so they are an addition rather than an alternative.
Get a specification for your building
We install all of these, so we have no reason to favor one. Call (346) 775-9128 or request a free estimate and we will tell you what your house needs.