Made from flexible vinyl polymers, these bird molds can be filled with plaster, clay or PerfectCast®, the durable compound used by museum professionals (available from Acorn Naturalists). Use the track cast positives you make from these molds (negatives) as instructional aids, pressing the tracks into moist sand or dirt, or use to make ink prints, or compare your impressions with ones found in the field. Everyone can have fun making tracks—students or campers can take them home or make displays. Clean with soapy cleansers occasionally as needed. Each mold also features the name of the track reversed out so that it appears correctly on the positive.