Trimethylpentyl Polysilsesquioxane
AKA “Isooctylsilsesquioxane, cage mixture
Ingredient
Ingredient Facts
Trimethylpentyl polysilsesquioxane
AKA: Isooctylsilsesquioxane, Cage mixture
Ingredient · Nail Conditioning · EWG: 4
Synthetic
Skin Conditioner
Not Clean
Trimethylpentyl Polysilsesquioxane is a resinous material composed of a mixture of three-dimensional siloxane polymers and oligomers with cage structures. For the oligomers, each silicon atom in the polysilsesquioxane is connected via oxygen atoms to three other silicon atoms and can be represented by the empirical formulation RSiO3/2 where R represents the trimethylpentyl group. For the larger polymeric polysilsesquioxanes, some of the silicon atoms are not connected to other silicon atoms and
CAS #
190732-67-3, 444619-08-3
Form
Liquid
See origin →
Functions
Nail Conditioning
A catch-all term for ingredients that improve how skin looks and feels — softer, smoother, more supple. The workhorse behind most moisturizers.
UV Protection
Strengthens nails
Traditional Use
A modern synthetic silicone-derived polymer developed for cosmetics to provide a lightweight, non-greasy feel. Creates a silky texture and improves product spreadability in makeup and skincare.
Skin Types
all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Yes
EWG
4
CIR
Safe as used
Pregnancy
Yes
CIR Safety Findings
Not a Sensitizer
medical-approval
all-shades-safe
Regulatory Status
USApermitted
EUrestricted
JAPANrestricted
CANADArestricted
Verified Jun 2026
Data: CosIng · EWG · CIR