Cofibrant operads and universal E∞ operads

We introduce various homotopy structures on the category of operads, which shed some light into the homotopy theoretic nature of the barconstruction WB of an operad, the whiskering process for operads and the Σ-freeness condition. Using the lifting property of cofibrant objects, we construct E∞ operads A which are universal: any E∞-structure lifts to an A-structure, canonically up to homotopy through A-structures.