You can set two factors for each material, a Bulking Factor and a Compression Factor. These materials affect the volumes added or removed to the ground or a structure. By default, factors are set to 1.0, but they can be changed. If you have set these factors for the Global Materials list, those factors will be used for each project but can be changed.
Sometimes, when material is moved from the ground it can swell up to occupy a larger volume. You can use the Bulking Factor to indicate the extent of this bulking.
For example: If a material has its Bulking Factor set to 2.00, when that material is Cut from the soil the volume will be double.
Sometimes, when Material is added to the ground it can settle, shrink, or be compacted to be a smaller volume. You can use the Compression Factor to indicate how material behaves in this circumstance.
For example: If you are importing material from offsite, you can set the Compression to 0.5, so that the imported material will halve in volume when it is put into the ground.
If you are reusing material, the Bulking Factor will be calculated first and then the Compression Factor applied next.
For example: If the materials Bulking Factor is 2, the Compression Factor is 0.5, the reused material will be half of the banked volume and a quarter of the bulked volume.