Compressibility is primarily influenced by which aspect of the material?

Compressibility in pharmaceutical materials, particularly powders, is primarily influenced by the solid fraction (or porosity) and compaction pressure. When discussing compressibility, it refers to the ability of a powder to decrease in volume under pressure.

The solid fraction indicates how densely packed the particles are in a given volume, which directly affects how much space is available for the particles to rearrange when subjected to compaction. High porosity generally leads to higher compressibility because more air is trapped within the powder bed, offering more voids for particles to collapse into under pressure.

Compaction pressure also plays a crucial role, as higher pressures encourage particles to come closer together, leading to increased contact points and interaction between particles. This results in a denser product and significantly affects the final mechanical properties of the compressed tablet.

While the other factors listed in the other options can influence certain properties of powders or tablets, they do not primarily drive the compressibility as effectively as the combination of solid fraction and compaction pressure does. For example, moisture content and temperature can affect the flowability and cohesion of powders but are secondary to the fundamental interactions highlighted in the correct answer.