Acoustic treatment made by additive manufacturing

A gas turbine engine comprising:

• a fan delivering bypass air into a bypass duct defined in part by a fan case as bypass air, a fan duct surrounding said fan;
• the fan also delivering core air into a compressor section, and the compressor section delivering air into a combustor, a turbine section mounted downstream of said combustor to receive products of combustion and to drive the fan and a compressor rotor;
• there being an interior surface of said fan case, and the interior surface including an acoustic treatment having a cell with the acoustic treatment having a sheath having a plurality of perforations;
• a plurality of cell structures extending from the sheath such that said sheath and said cell structures are a monolithic component, wherein the plurality of perforations of the sheath are formed by filaments of a first material that define a first dimension of the perforations having a linear edge and filaments of a second material crossing the filaments of the first material that define a second dimension of the perforations having a linear edge, the plurality of such perforations having a non-cylindrical shape defined by the linear edges of the filaments of the first material and the filaments of the second material;
• wherein strong areas of additional strength in at least one of said sheath and said plurality of cell structures are provided by in-fill materials added into a base material;
• wherein distinct radial areas are defined within a radial thickness of the sheath, and the material of the acoustic treatment including different characteristics in different areas;
• and
• wherein there being areas of increased strength with lower strength in other areas.