The best pure white background - depends on the target size to shoot. A jewelery need a piece of copy paper curved behind the product. A dress need a bed sheet. All of them must be wrinkle free and have to be equally well lighted with light source(s) between 4500 - 6500 °K color temperature. Most of the photo lights fulfill this requirement. Finally, in DoP you have to chose a white point with the color picker pipette under White Balance.
Generally the background whiteness is less important than the lighting source color temperature.