Humidity in Incubator.

What is a good way to create humidity in a refigerator being used as an incubator. I have seen people using bottles of water in their incubators but i do not understad how that creates humidty. The only way i understand it to work is if there is a hole in the bottle allowing vapor to exit when heated. Can anyone explain?????

the bottled water isn't for humidity its to regulate the temps. water releases its heat much slower than air, so should your power go out the water bottles will keep the temp up for longer. as far as raising humidity I use a large deli cup with the holes in the sides. I fill it with water and put it in the incubator. it only keeps my humidity around 50% so im not sure if it really helps that much.

Water bottles are used for stabilizing temps. The egg BOX humidity is what counts. You want it as high as you can get. I use substrateless method with Press N Seal under lid. I take it off 2 weeks before hatch date. Works great -- never a dry egg. Good luck.