Question: how to make fluffy slime rainbow?
Answer: In a large bowl mix glue and shaving cream with a spoon.
In a separate bowl or cup, mix 1/2 teaspoon of borax in 1 cup of water. ... 
Add about a teaspoon of the borax and water mixture into the glue/shaving cream bowl and stir.
Knead with your hands and if it's too sticky, add a tiny bit more borax and water mixture.