Tech-ply
A specific brand name for 1/4in 5-ply Birch Plywood Underlayment that is sold in sheets of 4'x5' or 4'x8'. It is a superior core for lightweight strap shields. Most lumber yards are not going to know what Tech-Ply/Tecply is, so be prepared to refer to it as 1/4in 5-ply Birch Plywood Underlayment.
Links