Polyvinyl Acetate. It's used widely in concentrated form in the construction industry as well as, in a more dilute form, in art and craft applications (Elmers). It's thick, gooey, sticky and stringy. PVA can be mixed easily with other water soluble substances and poster paints etc.

PVA is water soluble prior to curing and only cures when entirely dried out. In fact, even once it's cured it is never fully waterproof and can still be broken down with hot water at this stage. PVA does not contain any hazardous irritants either. These characteristics make it ideal for messy play as it will wash off bodies, hair, and most clothing relatively easily. Having said that, it is real glue that is meant to stick things together and can take quite a lot of water and bathing to properly disperse. It therefore has a deserved reputation for being an 'advanced' level or 'risky' substance tried by the more intrepid and experienced wammers.

It's important to point out that, although it is non-toxic and therefore relatively safe to be covered in, it is not edible. As with all such substances you should always do a skin test before you use it and extra care must be taken with dunking or pouring large amounts over the head that airways are not blocked--especially in bondage games.

Washes away easily with water but does not tend to dilute evenly and tends to coagulate and clump rather like flour.