Stay Tape
Stay Tape™ is a sheer straight tape for use on all fabrics especially fine, sheer and knit fabrics where stabilizing and support is needed without adding extra bulk. It can be cut to a narrow width without fraying. 100% Nylon. Preshrunk. Washable & Dry Cleanable. Colorfast. 1/2" x 10 yard roll. 

This product is either by Collins or Dritz...the availability changes between manufacturers, but it is the same product that I love for staying knit shoulder seams in a 'bulk-less' manner.