Usually, flexible (moldable/bendable) materials are preferred for wearable applications. Also, instead of using traditional substrates with copper layers, it is preferred if you can print microwave circuitry (i.e. stripline, antennas, etc) using (inkjet) printing technology to achieve more durable prototypes. Some examples of bendable materials are textile materials, polyimide-based materials, and thin organic substrates

1) A 3 mm-thick felt substrate (with a relative dielectric constant of 1.3 and a loss tangent of 0.044) and a 0.17 mm-thick ShieldIt Super conductive textile from LessEMF Inc.

2) Flexible polyethylene terephtalate (PET) film can be used as substrate in GHz.

3) See the following paper:

thank you

Conventional flexible materials like teflon etc. Or as advancement, smart materials, polymide based materials, organic materials etc