Update biofoam.md

docs/files/recipes/biofoam.md

@@ -131,7 +131,7 @@ Yes. Casting solids or smooth surface might require a different process to preve
 ## Variations on this recipe
 
 - Add a **natural colorant** such as a vegetable dye or water-based ink (e.g. hibiscus, beetroot, madder)
-- Add **less glycerine** for a more rigid foam, more for a more flexible foam
+- Add **less glycerine** for a rigid foam, add more for a flexible foam (up to 1 part glycerine, 1 part gelatine and a dash of water)
 - **Stiffeners** such as fibres or natural debris may be added for more structure and reinforcement.
 - **Fillers** such as almond or sunflower oil, chalk or egg shells can be added to prevent additional shrinkage.