materialdb - Materials Database

air	Empty layer
water	Description of a solid block of material.
H2O	Description of a solid block of material.
heavywater	Description of a solid block of material.
D2O	Description of a solid block of material.
lightheavywater	Description of a solid block of material.
DHO	Description of a solid block of material.
silicon	Description of a solid block of material.
Si	Description of a solid block of material.
sapphire	Description of a solid block of material.
Al2O3	Description of a solid block of material.
gold	Description of a solid block of material.
Au	Description of a solid block of material.
permalloy	Description of a solid block of material.
Ni8Fe2	Description of a solid block of material.

Common materials in reflectometry experiments along with densities.

By name:

air, water, heavywater, lightheavywater, silicon, sapphire, gold
permalloy

By formula:

H2O, D2O, DHO, Si, Al2O3, Au, Ni8Fe2

If you want to adjust the density you will need to make your own copy of these materials. For example, for permalloy:

>>> NiFe=Material(permalloy.formula, density=permalloy.bulk_density)
>>> NiFe.density.pmp(10)  # Let density vary by 10% from bulk value
Parameter(permalloy density)