If you own a Greentek sponge cap, you'll need to prepare and soak sponges prior to your recordings. See below steps for the 2 different types of these caps.
Greentek 24- / 32-channel cap - Type 1
You need to fill 200 ml of water in the provided bottle, and add two teaspoons (that comes in the package) of regular table salt. A measuring spoon came in the package, but you can also use a regular teaspoon.
Stir the solution until it becomes homogeneous. Afterwards, pour the water from the bottle into a plastic box that also came with the package, and soak the sponges for at least 12 hours before usage. You can re-use the sponges and keep them in the solution between recordings.
Once in a while it's good to prepare a new solution and rinse out the sponges, due to hygienic reasons. If you know you won't be using the sponges for a while, dry them completely so they don't keep extra moisture and become moldy.
See how to mount the cap in the video below:
Greentek 64-channel net cap - Type 2
Add 5 spoons of regular table salt (about 30 grams) with the weighing spoon into 1 liter of water in the measuring cup. Then, stir with the stirring spoon to form a solution.
Removing the chin strip from the cap and soak the cap into the saline solution for about 5 min. Make sure that all the electrodes have been immersed in the solution. The connector should never touch any liquid.
Take the cap out from the solution and remove the excess solution from the cap with a towel. Next step is placing the cap on the participant's head!
After the measurement finished, disconnect the cap from the EEG device. Remove the cap for the subject’s head and release the chin strap from the cap. Soak the cap in clean water for about 5 min, take it out from water, and then dry the cap and sponges with a towel. Repeat the washing procedure for another two times.
Hang the cap to dry in air and keep away from direct sunlight.