The full interaction between formaldehyde and He-4 atoms has been obtained from a first-principle calculation of the forces at play. In order to describe the nanoscopic features of HCHO being solvated in a quantum liquid, further Monte Carlo calculations for the system HCHO@He-N with N up to 20 have been carried out. The energetics and structure of the systems, as N changes, are extensively analyzed, and the excluded volume ("bubble") created by the inner cage that surrounds the solvated molecule is described and discussed to provide molecular microsolvation details for the title system.