Replacing Tinosorb M (MBBT) with BEMT (Bemotrizinol) in your silicone-based W/O emulsion is a highly recommended move and will likely resolve the issues you are experiencing.

1. Will this substitution solve the grittiness and sedimentation?

Yes, it is very likely to solve both issues for the following reasons:

• Elimination of Surfactant Conflict: Tinosorb M is a water-dispersion that uses Decyl Glucoside as a stabilizer. Decyl Glucoside is a high-HLB (O/W) surfactant. In a Water-in-Oil (W/O) system like yours (using SiliSolve™ and Hectorite Gel), adding an O/W surfactant into the internal water phase often causes emulsion instability, leading to "stickiness" and potential phase separation or "bleeding."
• Removal of Particulates from the Water Phase: Tinosorb M consists of organic micro-particles. In a W/O emulsion, these particles are trapped inside the internal water droplets. If the droplets are not perfectly uniform or if the emulsion is destabilized, these particles can aggregate, leading to the "grittiness" you observed.
• Oil-Phase Integration: BEMT is oil-soluble. By moving it to the oil phase, you eliminate the particulate matter in the water phase. Since it dissolves completely in solvents like LipidSoft™ C1215, the grittiness caused by undissolved particles will disappear, provided it is fully dissolved.

2. SPF and PA Value Estimation

Based on your proposed filter system:

• DHHB Ultra-Pure™ (UVA Filter): 5%
• Ethylhexyl Triazone (EHT) (UVB Filter): 4%
• BEMT (Broad Spectrum): 2%

Realistic Expectations:

• SPF (UVB Protection): You can realistically expect an SPF of 30 to 50. EHT at 4% is a very strong UVB filter, and BEMT at 2% provides significant additional UVB coverage.
• PA (UVA Protection): You can expect PA++++. DHHB at 5% typically provides PA+++ on its own; the addition of 2% BEMT (which is an excellent UVA I/II absorber) will easily push the protection into the PA++++ range.

Formulation Tips for Success:

1. Solubility Check: EHT has a relatively low solubility in C12-15 Alkyl Benzoate (approx. 4.4%). Since you are using 4% EHT in the total formula, ensure your oil phase has enough LipidSoft™ C1215 or other polar esters to keep it in solution. If the oil phase is too heavy on silicones like Silicone Gel Ultra Clear, the filters might recrystallize over time.
2. Heat Management: Your plan to premix at 60–70°C is correct. Ensure all three powders (DHHB, EHT, BEMT) are completely clear and transparent in the oil solvent before emulsification.
3. W/O Stability: To further ensure the stability of your W/O emulsion and prevent sedimentation of the water phase, it is highly recommended to add 1% Magnesium Sulfate to the water phase. This helps "lock" the water droplets in place within the silicone/oil matrix created by SiliSolve™ and Oil-Fix™ W.