Advice on your Bi-Phase Serum Formula

Here is a summary of the advice regarding your bi-phase serum formula:

• Glycerin Choice: You can use any of the three types (Glycerin, X-Glycerin, MOIST24). X-Glycerin and MOIST24 offer higher efficacy but are more expensive than standard Glycerin. Double Glycerin is not more effective than standard Glycerin and is typically used in oil-only formulas where other Glycerin types cannot be incorporated. For your formula with a water phase, standard Glycerin, X-Glycerin, or MOIST24 are suitable.

• Emulsifier: This formula does not require an emulsifier because it is designed to be bi-phase (separate layers). Xanthan Gum is used as a thickener at a low concentration (0.3-0.5%) to temporarily hold the oil and water phases together after shaking. The amount of Xanthan Gum affects how long the mixture stays combined before separating again.

• Preservative: Yes, sodium benzoate is used as a preservative. Mild Preserved Eco is considered gentler. However, sodium benzoate has a long history of safe use, including in food, and is considered highly safe at regulated concentrations due to its high purity manufacturing process.

• Xanthan Gum Function: In this formula, Xanthan Gum primarily functions as a thickener to help temporarily suspend the oil phase within the water phase after shaking, allowing the product to be used as a combined serum before the layers separate again upon standing.

• Comparison to Skin Barrier Cream: The Skin Barrier Cream recipe from Skin Recipe is significantly more effective at restoring skin moisture. However, its cost is much higher due to the selection of high-efficacy ingredients without prioritizing cost-effectiveness. If you prefer the performance of the barrier cream, you could modify that recipe by reducing the concentration of some ingredients or removing expensive ones to lower the cost.