In the tub
Layered tubs do something single colours cannot: they give the first ten minutes a goal. Children either keep the stripes separate for as long as possible or destroy them immediately, and both are entertaining to watch.

Compound Kings Butter Cloudz slime tubs
4.7 out of 5
$14.99
Ready to ship · price last read at the partner store
Three colours layered in one tub, the way the ice cream brick does it. Pull from one side and you get strawberry; fold the whole thing and you get a marble that never repeats.
Texture, scent and the sensible way to live with it.
Layered tubs do something single colours cannot: they give the first ten minutes a goal. Children either keep the stripes separate for as long as possible or destroy them immediately, and both are entertaining to watch.
Once folded, the marble holds. The pigments are dense enough that they stay distinct through dozens of pulls rather than turning into the brown that most three-colour slimes end up as.
Press the lid down after every session and keep it out of sun and off a radiator. Air is what shortens a tub's life; age is not. A stiff rim kneads back into the soft middle, and a tub that has set through is finished — water and lotion make it worse rather than better.