Tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate is a chemical compound used as a polymer stabilizer in plastics.

Like other hindered phenols it acts as a primary antioxidant.

It is formed by the Mannich reaction of 2,6-di-tert-butylphenol, cyanuric acid, and formaldehyde.

Tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate is a high molecular weight additive, with low volatility.

It is well suited to stabilising polyolefins against degradation caused by long term heat aging.