Physical Sunscreen Formulation Review

Based on the ingredients and percentages provided, this formulation for a physical sunscreen is feasible and aligns well with your desired properties:

• Texture: Using Milk Lotion Maker™ at 4% is suitable for creating a liquid, milky lotion texture that is easy to spread, as you requested. The liquid form of Titanium Dioxide 15nm Liquid and Zinc Oxide 35nm Liquid also contributes to a fluid consistency.
• White Cast: Both Titanium Dioxide 15nm Liquid (15nm) and Zinc Oxide 35nm Liquid (35nm) are nano-sized dispersions designed to minimize or eliminate white cast, so the result should be lightweight and not leave a white appearance on the skin.
• SPF/PA: The combination of 25% Titanium Dioxide 15nm Liquid and 15% Zinc Oxide 35nm Liquid is a robust physical filter system. These concentrations are typically used to achieve high broad-spectrum protection, likely reaching SPF50 PA++++, although actual testing is required to confirm the exact SPF and PA values.
• Water Resistance: WaterGuard™ Lite at 5% is included to provide some level of water and sweat resistance by forming a thin film. While not strongly waterproof, it should offer the slight resistance you are looking for. The water-in-oil emulsion system created by Milk Lotion Maker™ also inherently provides better water resistance than oil-in-water emulsions.
• Preservation: Mild Preserved Eco™ at 1% is a suitable preservative for this type of cosmetic formulation.

Mixing Procedure:

To successfully create this emulsion, you should follow a water-in-oil (W/O) process, similar to the examples provided for the sunscreen actives:

1. Combine the oil phase ingredients: Titanium Dioxide 15nm Liquid, Zinc Oxide 35nm Liquid, Milk Lotion Maker™, and WaterGuard™ Lite. Heat this phase to around 70°C while stirring until fully dispersed/melted.
2. Heat the water phase (Purified Water) to a similar temperature (around 70°C).
3. While blending the water phase at high speed, gradually add the heated oil phase. Continue blending as the mixture cools down to form the emulsion.
4. Once the emulsion has cooled sufficiently, add Mild Preserved Eco™ and blend until fully incorporated.

Overall, the formulation is well-designed to meet your requirements for a lightweight, non-whitening physical sunscreen with high protection and slight water resistance. Ensure accurate measurements and follow the appropriate W/O emulsification technique for best results.