Slacklining is an activity of air equilibrium which offers a wide range of practices from a mere leisure shared with friends in a park or as urban contest (Jumpline) to an extreme experience in high altitude (free solo). Vertiginous heights or fear of falling transform the gaming area into a felt void. This immateriality creates an inflexible feeling against which the consciousness is harmless. The body then ecologyzes itself without founding any solid marks (external or internal). The void, thanks to its sensorial deepening, put us into a more genuine and more intimate space. This is the reason why slacklining such as other physical or mental vertiginous experiences is currently growing in our today society where falling is one of the strong symbol.