# Foam Plastic Insulation: Building Code Definition

> How the IBC 2009, IRC 2009 define foam plastic insulation, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/foam-plastic-insulation/
- Last updated: 2026-09-07
- Data source: Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IBC 2009, IRC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IBC 2009 Plastic (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 9 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Foam plastic insulation is a defined term in the International Building Code (IBC) 2009, in Plastic. The code's own words are: “A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a density less than 20 pounds per cubic foot (pcf) (320 kg/m3).” The IRC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 9 chapters of this corpus, most often in Plastic (IBC 2009), Building Planning (IRC 2009), Duct Systems (IMC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.

*Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Foam Plastic Insulation** — IBC 2009, Plastic:

> A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a density less than 20 pounds per cubic foot (pcf) (320 kg/m3).

![Labeled code-term definition diagram: Foam Plastic Insulation: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/foam-plastic-insulation/diagram-1344.webp)

*How the IBC 2009, IRC 2009 define foam plastic insulation, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

Two of the I-Codes in this corpus define **Foam Plastic Insulation**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IBC 2009 | [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) | A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a density less than 20 pounds per cubic foot (pcf) (320 kg/m3). |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insulating or acoustic purposes and that has a density less than 20 pounds per cubic foot (320 kg/m3) unless it is used as interior trim. |

## Where foam plastic insulation is used in the code

The term appears in 9 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) | IBC 2009 | 62 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 27 |
| [Duct Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/duct-systems.md) | IMC 2009 | 19 |
| [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 10 |
| [Exterior Walls](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md) | IBC 2009 | 6 |
| [Foundations](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/foundations.md) | IRC 2009 | 5 |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 4 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 3 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 |

### The term in use

How the code actually writes about foam plastic insulation, quoted from the 2009 text hosted here:

> These provisions shall govern the materials, design, application, construction and installation of foam plastic, foam plastic insulation, plastic veneer, interior plastic finish and trim and light-transmitting plastics.

— [IBC 2009 §2601.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md)

> Packages and containers of foam plastic insulation and foam plastic insulation components delivered to the job site shall bear the label of an approved agencyshowing the manufacturer's name, the product listing, product identification and information sufficient to determine that the end use will comply with the requirements.

— [IRC 2009 §R316.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md)

> Foam plastic insulation used as wall or ceiling finish in plenums shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E 84 or UL 723 and shall also comply with Section 602.2.1.5.1,602.2.1.5.2 or 602.2.1.5.3.

— [IMC 2009 §602.2.1.5](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/duct-systems.md)


## The terms foam plastic insulation is built out of

The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what foam plastic insulation covers:

- **[Cubic Foot](https://harth.build/resources/glossary/cubic-foot.md)** — IRC 2009: The amount of gas that occupies 1 cubic foot (0.02832 m3) when at a temperature of 60°F (16°C), saturated with water vapor and under a pressure equivalent to that of 30 inches of mercury (101 kPa).
- **[Agent](https://harth.build/resources/glossary/agent.md)** — IFC 2009: A person who shall have charge, care or control of any structure as owner; or agent of the owner; or as executor, executrix, administrator, administratrix, trustee or guardian of the estate ofthe owner: Any such person representing the actual owner …

## Foam Plastic Insulation: what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IBC | Plastic | |
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Plastic (IBC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Duct Systems (IMC 2009) | |
| Re-check the requirement that uses it | Fire and Smoke Protection Features (IBC 2009) | |
| Confirm the dependent definition | Cubic Foot | |
| Confirm the dependent definition | Agent | |
| Local amendment to any of the above | Jurisdiction's amendment list | |

**A research aid, not a code determination.** The authority having jurisdiction decides which edition and which amendments apply.

## Where can you explore related guidance?

- [Explore all glossary guidance](https://harth.build/resources/glossary.md)
- [Cubic Foot: Building Code Definition](https://harth.build/resources/glossary/cubic-foot.md)
- [Agent: Building Code Definition](https://harth.build/resources/glossary/agent.md)

## Sources and method

Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of foam plastic insulation?

The International Building Code (IBC) 2009 defines it in Plastic as: “A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a density less than 20 pounds per cubic foot (pcf) (320 kg/m3).” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.

### Which parts of the code depend on foam plastic insulation?

In this corpus the term is used across 9 chapters, led by Plastic in the IBC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.

### What is foam plastic insulation?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Plastic: “A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a density less than 20 pounds per cubic foot (pcf) (320 kg/m3).” It is defined in IBC 2009, IRC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.

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