The spray foam glossary — trade terms, translated

Last reviewed: August 4, 2026

Every trade has its shorthand, and foam’s shorthand shows up in quotes, inspection reports, and lender letters where guessing wrong costs money. Here’s the working vocabulary, defined the way we’d explain it across a tailgate — each term linked to the page where the full story lives.

The material

Open-cell foam — the soft, low-density type. Cheaper per inch, good sound absorption, but it can hold moisture like a sponge — which is why where it’s sprayed matters so much.
Closed-cell foam — the rigid, dense type. Insulates, air-seals, and blocks moisture in one pass, bonds hard to what it touches, and is the harder one to ever remove.
2-lb / 1.7-lb / 3-lb foam — density classes. 2-lb closed-cell is the everyday pole-barn material; 1.7-lb stretches further per set; 3-lb is the dense structural/roofing stuff that yields less coverage (the cost math).
Set — how material arrives: paired drums of the two chemicals that combine at the gun. A set of standard 2-lb closed-cell yields roughly 4,000–5,000 board feet, and set price is where market swings hit your quote.
Board foot — one square foot covered one inch thick. The trade’s billing unit: surface area × thickness = board feet. If a quote doesn’t reduce to this math, ask why.

The chemistry going right — or wrong

Cured — finished reacting: hard, stable, essentially inert. Knock on good foam and it knocks back.
Off-ratio — the two chemicals didn’t mix at the intended proportions. Off-ratio foam can stay gummy and keep smelling — permanently. It will not finish curing next month; removal is the fix.
Adhesion — the bond between foam and surface. Foam that let go can’t be re-stuck, and failed adhesion means the air seal you paid for is already broken.
Delamination — foam separating from its surface in sheets; usually moisture or a bad substrate underneath (what each symptom means).
Substrate — whatever the foam was sprayed onto: roof decking, studs, steel panels. Foam inherits its substrate’s condition — spray over damp or dusty material and you inherit the failure.
A side / B side — the two liquids that meet at the gun to make foam. The A side carries the isocyanate; the B side carries everything else — resins, catalysts, blowing agent, flame retardant. “Off-ratio” means the two didn’t combine in the right proportion.
Isocyanate (MDI) — the reactive chemical on the A side, and the one the safety guidance centers on: before the foam cures, it’s a leading chemical cause of workplace asthma. The exposure window is the spray and the hours after, not cured foam — what EPA said, and what’s current.

The building science

R-value — resistance to heat flow, per inch. Closed-cell runs about R-7 per inch — but note the 87% rule: the first two inches do most of the work.
R-value drift — the label R-value is a lab snapshot; aging moves it on gas-blown foams and temperature moves it on everything. What drifts, by how much, and the aged numbers the law requires.
LTTR — Long-Term Thermal Resistance: the standardized aged R-value estimate for closed-cell foams (slice-and-age testing under ASTM C1303 / CAN-ULC S770). The number to compare quotes on — why it exists.
Dew point — the temperature where air’s moisture condenses into water. The whole game of insulating metal buildings is keeping the dew point from landing where water can collect — the full mechanics.
Vapor retarder — a layer that slows moisture migration. Code cares about it in specific assemblies (IRC R806.5 is the roof-deck rule our condensation guide cites).
Thermal barrier — the fire-code layer (commonly ½” drywall) required between foam and living space — the IRC R316.4 15-minute rule that changes barndominium budgets.
Air sealing — stopping air leaks, not just slowing heat. It’s the thing closed-cell does that batts and blankets fundamentally don’t (the honest comparison).

The paperwork and inspection world

Moisture scan / survey / mapping — three names for one service: finding water inside foamed assemblies without demolition, usually by infrared (how it works).
ASTM C1153 — the standard governing infrared moisture location on roofs; the citation to look for on a scan report.
Lender flag — when a mortgage lender, insurer, or appraiser raises spray foam as an underwriting question. There’s a playbook, and demolition usually isn’t it.

The removal trade

Containment — sealing the work area in plastic sheeting under negative pressure so removal dust stays put. Real quotes have a line for it (what removal involves).
Nuisance dust — the industry’s classification for cured-foam dust: not hazardous, but a real irritant demanding respirators.
Residue layer — the thin bonded film foam leaves behind when it tears away. Chasing it to bare wood typically takes a thin layer of the wood too — the industry’s own guidance says so.
Cryogenic (dry-ice) blasting — shooting dry-ice pellets to make residue brittle and pop free; a real technique from the industry’s removal manual, and heavily marketed by removal firms.
Spud bar — the long pry-and-scrape bar crews drive between closed-cell foam and the deck. Removal is labor; this is what the labor looks like.
Competent Person — OSHA’s term for the on-site decision-maker on removal technique, protective equipment, and disposal.

Missing a term you’ve hit in a quote or a report? Send it through the form — defining it plainly is exactly the job of this page.