Vacuum General 1 1 1 1 (by definition) Helium Gases at 0 °C and 1 atm 589.29 1.000036 1.000036 1.000036 1.000036 Hydrogen Gases at 0 °C and 1 atm 589.29 1.000132 1.000132 1.000132 1.000132 Air at STP General 1.000273 1.000273 1.000273 1.000273 Air Gases at 0 °C and 1 atm 589.29 1.000293 1.000293 1.000293 1.000293 Carbon dioxide Gases at 0 °C and 1 atm 589.29 1.00045 1.00045 1.00045 1.00045 Liquid helium Other materials 1.025 1.025 1.025 1.025 Perfluorohexane (Fluorinert FC-72) Other materials 1.251 1.251 1.251 1.251 Water ice Other materials 1.31 1.31 1.31 1.31 TFE/PDD (Teflon AF) Other materials 1.315 1.315 1.315 1.315 Water Liquids at 20 °C 589.29 1.333 1.333 1.333 1.333 Intestinal mucosa (human) Other materials 964 1.3335 1.329 1.338 1.329–1.338 Cryolite Other materials 1.338 1.338 1.338 1.338 Cytop Other materials 1.34 1.34 1.34 1.34 10% glucose solution in water Liquids at 20 °C 589.29 1.3477 1.3477 1.3477 1.3477 Acetone Liquids at 20 °C 1.36 1.36 1.36 1.36 Ethanol (ethyl alcohol) Liquids at 20 °C 590.29 1.361 1.361 1.361 1.361 20% glucose solution in water Liquids at 20 °C 589.29 1.3635 1.3635 1.3635 1.3635 Polytetrafluoroethylene (Teflon) Other materials 1.365 1.35 1.38 1.35–1.38 Liver (human) Other materials 964 1.369 1.369 1.369 1.369 Sugar solution, 25% Other materials 1.3723 1.3723 1.3723 1.3723 Cornea (human) Other materials 1.387 1.373 1.401 1.373/1.380/1.401 Lens (human) Other materials 1.396 1.386 1.406 1.386–1.406 Silicone oil (nD25) Liquids at 20 °C 589.29 1.398 1.393 1.403 1.393–1.403 Ethylene tetrafluoroethylene (ETFE) Other materials 1.403 1.403 1.403 1.403 Sylgard 184 (polydimethylsiloxane) Other materials 1.4118 1.4118 1.4118 1.4118 Sugar solution, 50% Other materials 1.42 1.42 1.42 1.4200 60% glucose solution in water Liquids at 20 °C 589.29 1.4394 1.4394 1.4394 1.4394 Kerosene Liquids at 20 °C 1.44 1.44 1.44 1.44 Fused silica (a pure form of glass, also called fused quartz) Solids at room temperature 589.29 1.458 1.458 1.458 1.458 Polylactic acid Other materials 1.46 1.46 1.46 1.46 Carbon tetrachloride Liquids at 20 °C 589.29 1.461 1.461 1.461 1.461 Pyrex (a borosilicate glass) Other materials 1.47 1.47 1.47 1.470 Vegetable oil Other materials 1.47 1.47 1.47 1.47 Glycerol Other materials 1.4729 1.4729 1.4729 1.4729 Sugar solution, 75% Other materials 1.4774 1.4774 1.4774 1.4774 Poly(methyl methacrylate) (PMMA) Other materials 1.4896 1.4893 1.4899 1.4893–1.4899 Benzene Liquids at 20 °C 589.29 1.501 1.501 1.501 1.501 Halite (rock salt) Other materials 1.516 1.516 1.516 1.516 Plate glass (window glass) Other materials 1.52 1.52 1.52 1.52 Crown glass (pure) Other materials 1.52 1.5 1.54 1.50–1.54 Sodium chloride Solids at room temperature 589.29 1.544 1.544 1.544 1.544 Amber Solids at room temperature 589.29 1.55 1.55 1.55 1.55 PETg Other materials 1.57 1.57 1.57 1.57 Polyethylene terephthalate (PET) Other materials 1.575 1.575 1.575 1.5750 Polycarbonate Other materials 150 1.6 1.6 1.6 1.60 Flint glass (pure) Other materials 1.61 1.6 1.62 1.60–1.62 Crown glass (impure) Other materials 1.62 1.485 1.755 1.485–1.755 Carbon disulfide Liquids at 20 °C 589.29 1.628 1.628 1.628 1.628 Bromine Other materials 1.661 1.661 1.661 1.661 Flint glass (impure) Other materials 1.724 1.523 1.925 1.523–1.925 Sapphire Other materials 1.77 1.762 1.778 1.762–1.778 Arsenic trisulfide and sulfur in methylene iodide Liquids at 20 °C 1.9 1.9 1.9 1.9 Boron nitride Other materials 2.07 2 2.14 2–2.14 Tantalum pentoxide Solids at room temperature 589.29 2.15 2.15 2.15 2.15 Cubic zirconia Other materials 2.165 2.15 2.18 2.15–2.18 Potassium niobate (KNbO3) Other materials 2.28 2.28 2.28 2.28 Zinc oxide Other materials 390 2.4 2.4 2.4 2.4 Strontium titanate Solids at room temperature 589.29 2.41 2.41 2.41 2.41 Diamond Solids at room temperature 589.29 2.417 2.417 2.417 2.417 Titanium dioxide (rutile phase) Solids at room temperature 589.29 2.614 2.614 2.614 2.614 Silicon carbide (moissanite; 6H form) Solids at room temperature 589.29 2.65 2.65 2.65 2.65 Cinnabar (mercury sulfide) Other materials 3.02 3.02 3.02 3.02 Birefringent: nω = 2.905 nε = 3.256 Silicon Other materials 1200–8500 3.45 3.42 3.48 3.42–3.48 Gallium(III) phosphide Other materials 3.5 3.5 3.5 3.5 Gallium(III) arsenide Other materials 3.927 3.927 3.927 3.927 Germanium Other materials 3000–16000 4.075 4.05 4.1 4.05–4.1