I bet you were expecting these to be stain resistant too, but the key application of nanotech underwear is medical sensing according to Business Week.
The tight elastic waistband of underwear “has tight contact and direct exposure with the skin and it allows for direct sweat monitoring via the chemical-sensing electrodes. And it seems elastic is a hardy textile. Engineers at the University of California, San Diego Jacobs School of Engineering discovered that even after aggressive testing by stretching, folding and pulling, the chemical sensors printed on the elastic still retained their sensing ability and could detect hydrogen peroxide and NADH — two compounds that sensors in “smart’ systems will need to recognize.”
According to Professor Joseph Wang, from the Department of NanoEngineering at the University of California,
If, for example, an injured soldier went into shock, enzymes on the electrode would sense rising levels of the biomarkers lactate, glucose and norepinephrine. This would cause the concentrations of products generated by the enzymes to change — higher hydrogen peroxide, lower norepi-quinone, higher NADH and lower NAD+. This would cause the built-in logic structure to output the signal “1,0,1,0” which indicates shock and could trigger a pre-determined treatment response.
The obvious problem seems to be how to transmit the data back to base without constantly bathing ones reproductive parts in microwave radiation, and of course keeping any medical supplies fresh in what is a notoriously warm and humid part of the anatomy.
Still, it should make an interesting and amusing change after sitting though years of conference speakers demonstrating the stain resistant properties of nanotech textiles using a glass of red wine (and sometimes ruining a carpet in the process).