Hello Taya, many thanks for your question. Slime is a fascinating substance and the best way of producing it is to mix a substance called Borax, with a substance like PVA with some water. There are other ways to do it but this is the traditional way. Is slime a liquid or solid? How do we measure how ‘liquid’ something is. We use a measure of the way a liquid pours, or if you drop something (a small metal ball) into it …how quickly it falls through it. This property of liquids is called it’s viscosity. Like most scales of measurement there are usually two extremes and something in the middle can have a little bit of both of the properties of a solid and a liquid – the slimes.
The Viscosity Scale was established by Newton in (would you believe it 1770 -almost 250 years ago). Slimes are registered as a Non-Newtonian fluids .
Why Borax and PVA? PVA is a substance called a polymer. A polymer is a long molecular particle of repeating units. Polymers usually quite happily slide over each other (not very viscous). Add borax and it’s molecules attach themselves to the PVA polymers and stop the easy sliding. Thus a slime is produced.
Uncertain about things in this answer. Please ask more. You can also look at this previous answer to a similar question.