Peptides are transported as a sterile filtered white lyophilized (freeze-dried) powder. Any research peptide can be light and fluffy, compact, dense tiny rocks or a small dense speck or a barely visible spray. There are several different reasons this can occur. To better understand, take a breif look into the steps of manufacturing.
1) Equal amounts of peptide by weight are deposited in a vial via machine.
2) The vial is partially stoppered and transported inside the lyophilizer.
3) The contents of the vial are then exposed to the nitrogen flush and air turbulence is created. The peptides may settle in different patterns during this step.
4) Vials are stoppered fully in the lyophilizer.
The components of the freezing cycle can vary from vial to vial very easily. The rate and manner of a freeze cycle can effect the physical form of the substance being frozen. For example if the freezing is slightly slower it can lead to formation of large ice like crystals and tight very dense compaction of the peptide. Adhesion to the sides of vials can happen when water vapor escapes during a process where it goes from a solid to a gas without ever going through a liquid phase. This characteristic will leave very little material to be seen by the naked eye.
The peptide temperature, the condenser temperature, chamber pressure, condenser pressure all may vary minutely between vials and account for the visual difference of the freeze-dried product between vials. All of these cycle parameters, the shelf freeze temperature, the product freeze temperature, the freezing "soak" time, the primary drying shelf temperature, cabinet pressure, product temperature for establishment of fill vacuum, secondary shelf drying temperature, and secondary drying time all may contribute to visually different appearance of vial contents if they very even slightly between vials.