All plastic soda or "pop" bottles start as a small plastic tube called a preform. When this preform is heated and blown into a bottle shape, it is ready to be filled with your favorite carbonated beverage. Our preforms come with full-sized final threaded openings so they use standard plastic soda bottle tops (included). Use them for a problem-solving activity by seeing if your students can guess their use. All bottle caps may be used again and again. These preforms are air and water tight when covered tightly with a bottle top and so are perfect for collecting or storing liquid samples.