Silk protein is a popular hair-care additive because it can improve slip, shine, manageability, and moisture retention. In shampoo bars, the key is choosing the right form of silk protein and adding it at a stage where it won’t be destroyed by heat or high pH.

Choose the right silk protein form

  • Liquid hydrolyzed silk protein - pre-dissolved and easy to use; add during the cool-down phase.
  • Powdered silk peptides or silk amino acids - concentrated, but must be pre-dissolved to avoid clumping.
  • Tussah silk fiber - mainly used in lye-based soap making, not a direct substitute for hydrolyzed silk protein.

Incorporating silk protein into syndet shampoo bars

Shampoo bars made with solid surfactants such as SCI, SLSa, and cocamidopropyl betaine are the best base for silk protein because their pH is closer to hair’s natural range. Follow these steps:

  1. Melt your solid surfactants and oils according to your formula.
  2. Cool the melted mixture to below 60°C (140°F) - or the temperature recommended by your silk protein supplier - before adding heat-sensitive proteins.
  3. If using powdered silk protein, first dissolve it in a small amount of distilled water, glycerin, or propanediol. Use just enough liquid to make a smooth slurry or solution.
  4. Add the dissolved silk protein or liquid hydrolyzed silk protein to the cooled surfactant mixture and stir gently but thoroughly.
  5. If your formula now contains added water, include an appropriate broad-spectrum preservative.
  6. Pour into molds and allow the bars to cool and harden.

A typical starting usage rate is 1-2% of the total batch weight, though some liquid silk proteins can be used up to 5%. Start low; too much can make the bar feel sticky or heavy on hair.

Incorporating silk protein into lye-based shampoo bars

If you are making a traditional cold-process shampoo bar, be aware that the high pH of lye soap can reduce the functional benefits of silk protein. That said, it can still add a smoother feel to the bar itself.

  1. Add liquid hydrolyzed silk protein at thin trace, after the oils and lye solution are fully emulsified.
  2. Use around 1-2% of the total batch weight, and account for any extra liquid if you are using a water-based silk protein.
  3. Stir well to distribute evenly before pouring.

Alternatively, some soap makers dissolve a small pinch of tussah silk fiber directly into the lye solution before mixing it with oils. This is a traditional method for adding silk to cold-process soap, but it is not the same as adding hydrolyzed silk protein.

Quick tips for best results

  • Avoid adding powdered silk protein directly to hot oils or hot surfactants; it will clump and may not disperse evenly.
  • Always follow the usage rate recommended by your supplier, and start with a lower amount.
  • If you introduce extra water into an otherwise anhydrous shampoo bar, adjust your formula and preservative accordingly.
  • Cooling the batch before adding silk protein helps preserve its film-forming and conditioning properties.