Immaterial art stock is a research project to preserve artworks created inside 3D digital spaces (such as Second Life, OpenSim, etc.). This project is initiated by the research program Spatial Media of Ecole nationale supérieure des Arts Décoratifs of Paris. The main objective is to establish a protocol and methodology to preserve this kind of art. Indeed, 3D digital artworks pose numerous challenges to the traditional art world. The fragility of these spaces, the changes in media and the program compatibility, require new model of preservation. In this paper, we present the project and issues raised. First of all, we will summarise digital conservation studies and describe specific nature of 3D digital artworks. Based on this, we present the components of the project.