Solid phases Helium remains liquid down to absolute zero at atmospheric pressure, but it freezes at high pressure. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) at about 25 bar (2.5 MPa) of pressure. It is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same. The solid has a sharp melting point and has a crystalline structure, but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30%. With a bulk modulus of about 27 MPa it is ~100 times more compressible than water. Solid helium has a density of at 1.15 K and 66 atm; the projected density at 0 K and 25 bar (2.5 MPa) is . At higher temperatures, helium will solidify with sufficient pressure. At room temperature, this requires about 114,000 atm.
solid phases helium remains liquid down to absolute zero at atmospheric pressure but it freezes at high pressure solid helium requires a temperature of 1–15 k (about −272 °c or −457 °f) at about 25 bar (25 mpa) of pressure it is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same the solid has a sharp melting point and has a crystalline structure but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30% with a bulk modulus of about 27 mpa it is ~100 times more compressible than water solid helium has a density of at 115 k and 66 atm; the projected density at 0 k and 25 bar (25 mpa) is  at higher temperatures helium will solidify with sufficient pressure at room temperature this requires about 114000 atm