This activity departs from what is conventionally done in that students do not solely determine the density of various isolated objects. Instead, students use the inherent property of 3D printing, infill, to test density. By adjusting the percentage of infill of a 3D printed object, represented in the form of a boat, students get to determine and control its density. They are able to observe the gradual effect this has on the boat’s ability to float not only in water but in other fluids. Students can design boats that float in water but sink in another fluid, or boats that are suspended within fluids. With the use of 3D printer students have the power to test multiple versions quickly and efficiently in the classroom. A similar lab that does not use 3D printing may require students to use materials to test density that are not water resistant (paper, wood) and require more time to construct into a testable object.