Explanation of Your Rinse-Off Mask Formula

Based on the formula you provided, which uses Light Cream Maker, Mineral Oil Light, Glycerin, Soy Extract, Phenonip P4, and Tween 20, the behavior you observed where the mask turns oily after about 10 minutes is expected for this type of formulation.

Your formula creates a standard oil-in-water (O/W) emulsion cream. When applied thickly as a mask, the water phase of the cream gradually evaporates from the skin surface over time. The oil phase, particularly the Mineral Oil Light which is present at a relatively high concentration (20%), is not fully absorbed into the skin. As the water evaporates, the emulsion structure on the skin surface can become less stable, leaving the unabsorbed oil feeling prominent and giving the sensation of an oily layer.

This is consistent with the previous explanation you received. This formula functions as a regular cream that leaves an emollient layer on the skin, rather than a specific rinse-off mask base designed to form a film or be easily washed away without leaving a significant oily residue.

Dedicated rinse-off mask bases are formulated differently to provide a texture that remains consistent during the wear time and is easily removed with water, often utilizing specific film-forming agents or different emulsification systems suitable for wash-off applications. As mentioned by the staff, specific bases for rinse-off masks are being developed.