There are standards for the dielectric and conductive properties such as for measuring SAR with a phantom head (Sam) filled with a liquid.
Typical ingredients (wt %)
900 MHz sugar: 57.90, water: 40.30, cellulose: 0.24, NaCl: 1.38, Bactericide:0.18
1800 MHz water: 55.41, DGBE: 44.51, NaCl: 0.08
1900 MHz same as 1800 but no NaCl
Amount of sugar requires boiling water to solve.
DGBE can harm some plastics as it is a kind of ethanol, use good containers. Not fun to find 10 liters of sirup dripping on other RF equipment.
There are also other recipes for hand/torso/full body models.
If you not want to mix it yourself: **broken link removed**
These recipes have been discussed as they are designed for skinny models and designed very long ago and average people are fatter today.
RF in fat differentiates a lot compared to meat, bone and common body fluids.
RF for medical implants need to in more detail take account what kind of tissue that is in absolute nearfield. Tables exist.
Many RF modelling softwares have predefined detailed body models.