A pack of 20 plastic electrostatic strips, 10 made of clear Polycarbonate and 10 made of white Polystyrene. The Polycarbonate strips can be positively charged and the Polystyrene strips can negatively charged. Simply rub with a yellow duster and let the students work it out! By using the brass holders, the charged strips can be suspended from the string supplied and thus they are insulated/isolated from any earth.