Measure out the lye, coconut oil, and water, in separate containers using a digital scale.
Add the lye to the water, taking care to avoid breathing in any fumes. (NEVER add the water to the lye.) Stir with a butter knife to make sure all the lye dissolves. The solution will get very hot. Carefully set it aside to cool in a safe place.
Place the coconut oil into a pot and melt over medium low hot on the stovetop. The oils must be completely melted and 130-140 degrees before proceeding. Once it has reached the temperature, remove it from the heat and allow it to cool in a safe place.
Check the temperature of your oil and lye after an hour or two. You can use a thermometer or feel the side of the containers with your hand. They should be comfortably warm, but not at all hot.
Pour the lye solution into the melted oil pot and blend using a stick blender. The soap solution is very caustic at this point and can cause burns. Make sure you are wearing gloves and goggles. Have everything ready before you start. Blend until your soap reaches trace. This means that when you drag your blender through the solution, it leaves a trace. If you lift up your stick and soap batter comes off of it, it will not immediately flow back in like a liquid, but will sit on top for just a second, like a thin batter.
As soon as trace is reached, immediately pour the batter into the molds. If you take too long, soap will start forming and hardening right in the pot.
Put your mold out of the way somewhere to let the soap saponify (turn in to soap). It will need to sit about 12-24 hours
After the waiting period, turn the soap bars out and store them in a ventilated spot such as an old tea towel on top of a dresser. Allow to cure two weeks before using.