Neutrons with low enough kinetic energy (< 300 neV) are reflected by some materials due to the so-called Fermi pseudo potential. These ultracold neutrons can therefore be stored in an actual bottle made from an appropriate material (such as Nickel or Aluminum). Another approach is to use magnetic fields to create a potential well (neutrons have a magnetic moment) and to rely on gravity to keep them in that well. Ultracold neutrons behave very much like ping-pong balls and cannot jump very high (less than a few meters) due to their low velocities.