Aged R-value and what you should actually promise customers

It is May, the busy season is building, and somewhere in New York today a contractor is standing in a kitchen telling a homeowner that closed-cell foam is "R-7 per inch." Maybe R-7.5. He is not lying, exactly — he read it somewhere, or a rep said it years ago. But the number the homeowner's house will actually feel in five years is closer to R-6 per inch, and the gap between what was promised and what performs is where callbacks, bad reviews, and awkward phone calls come from.

Let's talk about where that gap comes from, because it is not a defect and it is not a scam. It is physics, it is printed on the data sheet if you know where to look, and the contractors who explain it up front sound smarter than the ones who quote the shiny number.

Why fresh closed-cell tests higher than aged closed-cell

Closed-cell foam gets its insulating power from the gas trapped in its cells. That blowing agent — these days usually a low-GWP HFO blend, since most closed-cell lines here switched over from HFCs by around 2022 — conducts heat much more poorly than air does. Fresh foam, full of blowing agent, insulates beautifully.

But cell walls are not perfect. Over months and years, blowing agent slowly diffuses out and air slowly diffuses in. Air conducts heat better than the blowing agent, so the R-value per inch drifts down and then levels off. This is why manufacturers publish aged R-values, measured on foam that has been conditioned to represent years of service. The aged number for closed-cell typically lands nearer R-6 per inch; fresh numbers can look meaningfully higher. Both are "true." Only one describes the wall your customer lives with.

Check the TDS on whatever system you are spraying. The aged or LTTR value is the one to build your promises on.

Why open-cell does not drift the same way

Open-cell foam is a different animal. It is water-blown, and its cells are open — the gas inside them is just air from day one. There is no exotic blowing agent to leak out, so there is nothing to drift. Open-cell sits at roughly R-3.5 to R-3.8 per inch and stays there. Lower number, but honest from the start.

That is worth saying out loud in a sales conversation, because customers who have done some reading may ask. "Open-cell is R-3.5 to R-3.8 per inch and holds it. Closed-cell starts higher and ages to about R-6 per inch, which is the number I quote." That sentence has never lost anyone a job.

The wall is not made of foam

Here is the second honesty gap, and it is bigger than blowing-agent drift: R-value per inch describes the foam at the center of the cavity. The wall is not all cavity.

Every stud is a thermal bridge. Wood runs somewhere around R-1.2 per inch — a 2x6 stud is roughly R-6.5 to R-7 through its full depth, while the foam beside it might be R-33-plus. On a typical framed wall, framing can be 20 percent or more of the surface area once you count studs, plates, headers, and window framing. Heat takes the easy path, so the whole-assembly R-value — the number the house actually experiences — lands well below the center-of-cavity number.

A rough worked example, and treat it as illustrative:

• 2x6 wall, 5.5-inch cavity filled with closed-cell at an aged R-6 per inch: center of cavity around R-33.
• Framing fraction around 23 percent, studs at roughly R-6 through their depth.
• Area-weight the two paths and the assembly lands in the mid-teens — high teens once you add sheathing, drywall, and air films.

That is not a knock on foam — the same thermal bridging hits fiberglass and cellulose walls too, and foam's air sealing is doing work no R-value test captures. But if you tell a customer "this is an R-33 wall" and an energy auditor later models it at R-20, you look like you either lied or did not know. Neither is a good look.

Quote the aged, assembly-honest number and win anyway

Here is the counterintuitive part: quoting the lower, honest number wins jobs. The customer getting three bids hears two contractors say R-7 per inch and one contractor explain fresh versus aged, cavity versus assembly, and why he quotes the conservative figure. Guess who sounds like the professional. Guess whose bid survives when the customer's engineer brother-in-law reviews it.

Some habits worth adopting:

1. Put the aged per-inch value and the installed thickness on the proposal. "3 inches closed-cell, aged R-value approx. R-18" beats a bare "R-21."
2. Never promise a specific energy-bill savings percentage. You do not control their thermostat, their windows, or their teenager's showers.
3. When a code target like R-49 in an attic is in play, spec the thickness from aged values, not fresh ones — and confirm the target with the local code official, because required values shift with code cycle and climate zone.
4. Keep the TDS for the exact product and lot in the job file. If a dispute ever comes, the document that saves you is the one with the published aged value you quoted from.

Overpromising is a loan you repay with interest

Every inflated number in a bid is borrowed trust. It gets repaid as a callback, a comfort complaint, a demand for "the R-value I paid for," or a blower-door test you have to argue with. The margin you protected by sounding better than the other bids evaporates the first time you roll a truck back to a job that is performing exactly as physics said it would.

Quote aged. Quote assembly-aware. Explain why in two sentences. It is the cheapest reputation insurance you can buy, and it costs you nothing but the discipline to say a slightly smaller number.

If you want help turning honest numbers into bids fast, the Winters Breath job estimator works from thickness and area, so you can price a wall at aged values on the tailgate — and every set we ship is tracked by drum serial, so the TDS you file matches the material you actually sprayed.