I had tried plstic bottles for solar ignition many times before. It finally dawned on me that the roundish shape of those bottles were not pronounce enough. When I happened to see the Smart Water Bottle in the store's cooler, I knew it would work. I bought it while at work. When I got home at 5pm it was really too late to try it because the sun was so low on the horizon. AND it was winter which mrans the sun was even farther away from the earth than desirable. Lol! I still wanted to try for the char cloth ignition. It took 5 minuutes, but I finally found the right angle, got the ignition, and the the flames. Fire making techniques is my hobby and I was glad to mark the water bottle solar ignition off the list.