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Nathalie is candid about not being certain of the exact SPF. One option would be to add a combination of Zinc Oxide and micronized Titanium Dioxide (not nanoparticles) to the recipe. Here is an organic zinc oxide and micronized titanium dioxide for sale on Amazon that has an SPF of 35: Bee Sunny SPF 35 Mineral Powder Sunscreen Zinc Oxide & Titanium Can
You’d have to experiment with the amount to add until you got a consistency you liked. Click on the Best Homemade Nontoxic Sunscreen Recipe Ever link below to see the complete recipe.