Gas turbine engine buffer system

A method of designing a gas turbine engine comprising:

• defining a compressor section;
• defining a combustor in fluid communication with the compressor section;
• defining a turbine section in fluid communication with said combustor;
• defining a fan section configured to be driven by a turbine section via a geared architecture;
• and
• configuring a buffer system for communicating buffer air to a portion of the gas turbine engine, wherein the buffer system is defined to include a first circuit for selectively mixing a first bleed air supply having a first pressure and a second bleed air supply having a second pressure that is greater than the first pressure to provide a first buffer supply air having an intermediate pressure compared to the first pressure and the second pressure.