Bitumen (bitumen) is a thick, black crude oil. Bitumen is a low-grade crude oil composed of complex, heavy hydrocarbons. In an oil reservoir, bitumen is a thick, viscous liquid and needs to be removed from the ground. When removing it, a lot of heat and effort must be expended to upgrade it to a better product.

The penetration test of bitumen measures the hardness or softness of bitumen by measuring the penetration depth of a standard loaded needle within five seconds while maintaining the bitumen sample temperature at 25 °C. The more viscous the bitumen, the less distance the needle can penetrate. Therefore, the penetration value for viscous bitumen is lower.
For example, if the needle enters between 6 and 7 mm in 5 seconds, we will obtain 60/70 bitumen.
Penetration is measured to determine the type of bitumen according to the climatic conditions of the region where the bitumen is consumed. This penetration depth is empirically (but only roughly) related to asphalt binder performance. For this reason, asphalt binders with high penetration numbers (called “soft”) are used for cold climates (such as 85/100) and asphalt binders with low penetration numbers (called “hard”) are used for hot climates (such as 40/50).