Skim through

What it does: antistatic, hair conditioning, surfactant/cleansing

The science

In itself, it's an antistatic (stops your hair from flying around because of electricity), hair conditioning and softening ingredient used mainly in haircare products. It is also useful for improving the feel of the product, making the product more spreadable and easy to handle.

Benefits for your hair

Reduces frizz

Behentrimonium methosulfate is used in hair care products as it reduces the friction between the hair shafts, adding slip and improving the general feel and manageability of the hair. 

Reduces breakage 

Reducing friction between the hair shafts also helps to reduce breakage and damage. When the friction between the hair strands is reduced, the hair is less likely to tangle and break.

TLDR 

Behentrimonium methosulfate conditions the hair and reduces frizz and breakage.