Skin Care Formulation Volume 10 Bath Bombs

Module 10 covers bath bomb formulation. Over 6 days, you will formulate 2 commercial-grade bath bombs, mastering acid-base effervescence, moisture management, and mold-packing physics.
Core Science
Acid-Base Effervescence: The core reaction relies on an acid and a base. Sodium bicarbonate (base) + Citric acid (acid) + Water (catalyst) = Sodium citrate + Water + Carbon dioxide (CO2 gas). The rapid release of CO2 creates the signature fizz.
Moisture Management (The Enemy): Citric acid and baking soda are highly hygroscopic. If they absorb ambient humidity, they react prematurely (pre-fizzing) and ruin the batch. Formulation and manufacturing must occur in low-humidity environments .
Binder Rheology: Liquid oils and butters coat the dry powders, providing cohesion for molding while delaying the water-acid reaction until the bomb physically hits the bathwater.
Raw Materials Covered
The Core Reaction:

• Sodium Bicarbonate: The base. Provides the bulk and the CO2 source.
• Citric Acid: The acid. Triggers the reaction. (Standard ratio is 2:1 or 1.5:1 base-to-acid).

• Cornstarch / Tapioca: Slows the reaction rate, softens the water, and adds bulk.
• Cream of Tartar: Acts as a hardener to prevent the bomb from crumbling.
• Kaolin Clay: Adds structural integrity and a silky feel to the water.

• SLSA (Sodium Lauryl Sulfoacetate): A mild, natural-derived foaming agent that creates a bubble bath effect. (Do not confuse with harsh SLS).

• Carrier Oils/Butters: Sweet almond oil, shea butter, or cocoa butter to bind the powders.
• Polysorbate 80: Crucial ingredient. It emulsifies the binder oils in the bathwater so they disperse evenly rather than floating to the top and leaving a greasy "ring around the tub."

• FD&C Lakes: Oil-dispersible pigments. Never use water-soluble dyes, as they will stain the bathtub.
• Micas: For shimmer (use tub-safe, lip-safe grades).
• Essential / Fragrance Oils: Must be skin-safe and IFRA compliant for wash-off body products.

1. Control Humidity: Work in a dehumidified room. If the mix fizzes while you are mixing it, the ambient air is too humid.
2. Always Use Polysorbate 80: Unless you want your customers slipping on a greasy bathtub ring, emulsify your binder oils.
3. The "Sandcastle" Test: The perfect moisture level feels like wet beach sand. It should hold its shape tightly when squeezed in your fist, but crumble easily when poked with a finger.
4. Add Liquids Slowly: Mix your wet ingredients (oils, fragrance, polysorbate) thoroughly, then drizzle them into the dry powders very slowly while whisking continuously.
5. Pack Hard: Compress the mixture tightly into both halves of the mold before joining them. Do not twist the mold halves, or the bomb will crack.
6. Dry Thoroughly: Let the bombs dry for 24-48 hours in a cool, dry place before unmolding or packaging.

• o staining) and "moisturizing without the grease ring" as your primary marketing differentiators.