Review of Your Proposed Physical Sunscreen Formula

You're looking to create a physical sunscreen with SPF 50-70 that is silicone-free, non-greasy, and easy to make without heat, suitable for outdoor use with acceptable whiteness.

Your initial proposed formula is:

1. Zinc Oxide 200nm EasyDisperse (20%)
2. Titanium Dioxide 200nm EasyDisperse (10%)
3. MatteSilica (3%)
4. LipidSoft Lite (66%)
5. Mild Preserve Eco (1%)

Mixing steps: Mix 1, 2, 3 in LipidSoft until dispersed, then add 5 and mix.

Feasibility of No-Heat Method for High SPF Physical Sunscreen

Based on the information available, achieving a high SPF (50-70) with a physical sunscreen generally requires proper and even dispersion of the Zinc Oxide and Titanium Dioxide particles throughout the formula. For many physical sunscreen ingredients, especially powders, this optimal dispersion is best achieved with the application of heat and sufficient mixing/homogenization.

The staff reply also indicated that sunscreen formulas often require heat to effectively disperse ingredients and achieve high SPF. While the "EasyDisperse" versions of Zinc Oxide and Titanium Dioxide are designed for easier mixing, the description for Titanium Dioxide 200nm EasyDisperse specifically states it's for makeup products and recommends selecting from the "Titanium Dioxide for UV Protection" category for sunscreens. This suggests that while it disperses easily, it might not be optimized for high SPF performance compared to dedicated sunscreen grades.

Attempting to create a high SPF physical sunscreen by simply mixing powders into an oil phase without heat or specialized equipment may result in uneven particle distribution, leading to reduced and inconsistent sun protection.

Alternative Approach with Heat

Your second proposed approach, mentioning the use of heat with Titanium Dioxide 15nm Liquid (20-25%) and Zinc Oxide 200nm EasyDisperse (5%) along with Milk Lotion Maker and emollient, aligns better with the typical methods for creating stable and effective physical sunscreens with high SPF.

• Titanium Dioxide 15nm Liquid: The description for this product indicates it's a liquid dispersion designed for easy mixing into cream recipes with heat (70°C) and stirring to achieve high effectiveness. It is a dedicated sunscreen grade.
• Zinc Oxide 200nm EasyDisperse: This can be used in sunscreen formulas, and its description mentions mixing in silicone or oil. While the 15nm liquid Titanium Dioxide is recommended for minimal whiteness, the 200nm Zinc Oxide is noted as giving low whiteness and is suitable if you want to claim non-nano Zinc Oxide.
• Milk Lotion Maker: This is an emulsifier suitable for oily formulations, especially sunscreens, and is used in a sample sunscreen formula provided in its description that involves heating the oil phase.
• LipidSoft Lite: This emollient is suitable for lightweight, non-greasy formulas and can be used in place of oil. It's compatible with the ingredients.
• MatteSilica: This ingredient helps absorb oil and provides a matte finish, which aligns with your goal of a non-greasy product. It can be added in the final step.
• Mild Preserve Eco: This is a suitable preservative that can be added in the final step.

Using heat to combine the oil phase containing the dispersed physical sunscreens and the emulsifier, and then emulsifying with the water phase (if creating an emulsion), is the standard method to ensure proper dispersion and stability for a physical sunscreen aiming for high SPF.

Recommendation

Given your goal of SPF 50-70 and the desire for a stable, effective physical sunscreen, the approach involving heat with dedicated sunscreen-grade ingredients like Titanium Dioxide 15nm Liquid and Zinc Oxide 200nm EasyDisperse, along with a suitable emulsifier like Milk Lotion Maker, is more likely to be successful than a simple no-heat mixing method with the initial ingredients chosen for the no-heat attempt.

You should follow the mixing instructions provided for Titanium Dioxide 15nm Liquid and Milk Lotion Maker, which involve heating the oil phase and emulsifying with the water phase while stirring. Incorporate LipidSoft Lite in the oil phase, and add MatteSilica and Mild Preserve Eco in the final steps as per their general usage guidelines.

Remember that achieving a specific SPF level requires testing, and the provided percentages are starting points. The combination and concentration of UV filters, along with the formulation method, significantly impact the final SPF and PA values.