A conditioning agent (like Incroquat BTMS-50) is a cationic quaternary compound. It's a positively charged compound that adsorbs to the surface of your hair. (Adsorption means the molecules accumulate on the surface of your hair. It's different from absorption in that it doesn't penetrate, it just sits on top of the hair fibre.) This is called substantivity.
Substantivity is defined as "an adsorption phenomenon by which materials that have opposing charges or like composition are more readily adsorbed onto or attracted to its surface and, once there, resistant to subsequent rinse-off." In other words, a material that is positively charged - like our cationic ingredients - will be attracted to the surface of our hair, which is negatively charged.
The cationic quaternary compound is hydrophobic - "scared of water" - so it will resist removal by water alone. (The more hydrophobic the quaternary compound, the less likely it is to be removed by water alone.) So the positively charged cationic quaternary compound is attracted to your negatively charged hair fibre and clings on to the surface.
Being resistant to rinse-off doesn't mean it won't come clean and cause build up; it just means it won't rinse off when you rinse your hair after applying the conditioner. It will rinse off when you wash your hair with shampoo in the future. If you are worried about build up of styling products, consider adding cetrimonium chloride to your products - 2% is enough!
Cationic quaternary compounds increase the lubricity, static control, and combability (is that a word?) of your hair. It's always a good thing to have extra moisturization in your hair, increasing the water content on the hair fibre, and increasing the lubricity of our hair. By doing these things, you're reducing the force required to comb or brush your hair, which means fewer broken or torn out hairs and less static electricity on the surface!
If you are using a product that is negatively charged (anionic) or neutrally charged (non-ionic) as a conditioner, it will not offer substantivity to your hair. So something like apple cider vinegar (non-ionic, acidic) will not adsorb to your hair strands, which means it won't increase the conditioning of your hair, which means you aren't reducing the combing forces and the friction to your hair. Oils (non-ionic, neutral pH) will coat the hair strands to increase lubrication and moisturization, but they aren't substantive, so by definition they aren't conditioning. They still offer some awesome features to our products and our hair, but they aren't conditioning.When formulating a conditioner, we want maximum adsorption and maximum substantivity to get the most out of the product. We do this by choosing a cationic quaternary compound that will adsorb to our hair, like Incroquat BTMS or cetrimonium bromide. The cationic quaternary compound is always the basis from which we work when creating a great conditioner.
We can increase our substantivity by adding a fatty alcohol, like cetyl alcohol, to the mix. Fatty alcohols increase the substantivity of the conditioner by adsorbing to the hair fibre as well and encouraging more adsorption by the quaternary compound. And we add all the other goodies like hydrolyzed proteins, oils, butters, silicones, and so on to increase the substantivity, adsorption, and moisturization of our hair.