# Polyisobutylene (min M W 37,000)

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**Safety rating:** SAFE
**CAS number:** 9003-27-4
**Category:** other
**FDA GRAS:** no
**Adverse events (FDA AERS):** 0
**FDA recalls:** 0
**Last updated:** 2026-04-04

## Summary

Polyisobutylene (PIB) is a synthetic polymer used as a masticatory substance in chewing gum and related products. With a minimum molecular weight of 37,000, it functions as a gum base component that provides elasticity and texture without being metabolized or absorbed by the body.

## Regulatory status

| Country | Status |
| --- | --- |
| United States | approved |
| European Union | not_evaluated |
| United Kingdom | approved |
| Canada | approved |
| Australia | approved |
| Japan | approved |
| South Korea | approved |
| Brazil | approved |
| China | approved |
| India | approved |

## Detailed analysis

## What is Polyisobutylene?

Polyisobutylene (PIB), identified by CAS Number 9003-27-4, is a synthetic polymer composed of isobutylene monomers. The specification "min M W 37,000" refers to its minimum molecular weight of 37,000 Daltons, which ensures the material remains as a high-molecular-weight polymer unsuitable for absorption through the gastrointestinal tract. PIB is a colorless, odorless, tasteless substance that exhibits rubber-like properties, making it suitable for food applications requiring elasticity and chewability.

## Common Uses

Polyisobutylene is primarily used as a masticatory substance in chewing gum formulations. It serves as a key component of gum bases, providing the characteristic texture and elasticity that allows gum to be chewed without disintegrating. The high molecular weight specification ensures the polymer remains insoluble in saliva and digestive fluids, meaning it passes through the digestive system intact without being broken down or absorbed. This property is essential for its safety profile in food applications.

## Safety Assessment

Polyisobutylene with a molecular weight of 37,000 or higher has not been associated with adverse health effects in food applications. The polymer's large molecular size prevents gastrointestinal absorption, meaning ingested PIB does not enter systemic circulation. The FDA has received zero adverse event reports associated with PIB use in food, and no recalls have been issued. Toxicological studies on high-molecular-weight PIB indicate it poses minimal risk when used as intended in chewing gum and similar masticatory products.

The safety of PIB depends critically on maintaining the specified minimum molecular weight. Lower-molecular-weight variants might present different safety considerations and are not approved for food use under this specification. The inert nature of high-molecular-weight PIB, combined with its inability to be absorbed or metabolized, contributes to its favorable safety profile.

## Regulatory Status

Polyisobutylene (min M W 37,000) is not listed as a Generally Recognized As Safe (GRAS) substance by the FDA, meaning it does not benefit from GRAS self-affirmation status. However, it may be used in food under FDA regulations if it meets applicable requirements for food additives and was in use prior to certain regulatory changes, or if it has been approved through other regulatory pathways. The absence of GRAS status does not indicate safety concerns; rather, it reflects the regulatory classification and approval history of the substance.

Regulatory acceptance of PIB varies internationally. Some countries recognize it for use in chewing gum bases, while approval status may differ in other jurisdictions. Manufacturers using PIB must ensure compliance with applicable food additive regulations in their target markets.

## Key Studies

While comprehensive published literature on PIB in food applications is limited, the safety rationale is based on the fundamental principle that high-molecular-weight polymers cannot be absorbed through the gastrointestinal tract. This principle is well-established in food science and toxicology. Studies on structurally similar high-molecular-weight polymers used in food (such as other gum base polymers) support the safety of inert, non-absorbable polymers in food applications.

The zero adverse event reports and zero recalls in the FDA database provide additional real-world evidence of the safety record of PIB in commercial food use. Long-term use in chewing gum formulations has not revealed safety concerns in consumer populations.

## Sources

- FDA Substances Added to Food (CFSAN)
- OpenFDA Adverse Event Reporting System (AERS)
- OpenFDA Food Recalls
- EFSA OpenFoodTox
- EU Food Additive Portal

## Citation

Additive Facts. "Polyisobutylene (min M W 37,000) — Safety, regulation, and evidence." https://additivefacts.com/additives/polyisobutylene-min-m-w-37-000. Accessed 2026-05-20.