ith an increasing number of gel-based dermalfillers on the market, there is an increasinginterest in correlating the different properties, such asrheological and cohesive properties, with the clinicaleffects and uses. The rheological properties ofhyaluronan (HA) fillers have been explored for quitea long time, but more recently the discussions havebeen focused around the cohesive properties of HAfillers.Cohesion is described as the force between particles ofthe same substance that acts to unite them. In otherwords, it is easy to separate the particles in a lowcohesivematerial but more difficult in a material withhigh cohesion. In IUPACs Golden book,1 the definitionof cohesion is:Theworkof cohesion per unit area of a singlepure liquidor solid phase a,wac is the work done on the systemwhen a column a of unit area is split, reversibly, normalto the axis of the column to form 2 new surfaces each ofunit area in contact with the equilibrium gas phase.Currently, there are no ready-made instrumentsdesigned to measure cohesion, or methods whichcould be easily adapted to gels. Several manufacturersof HA gels have investigated their cohesive propertiesusing various different methods but as yet, unlikerheology, there is no standardized methodology that isacknowledged by the scientific community as a validway of evaluating cohesion.In a vast majority of articles where investigators stategels to be cohesive, no explanation is given on how this