We polymerized a glove, and looked if we could warm it with a bit of power, it's quite nice in winter!
With about 0.6A x 20V = 12W (yeah, not exactly low-power), the glove went from 20°C to 53°C (= from 68°F to 127°F) in about 9 seconds (it's not very comfortable above that temperature).
For scientific reasons, we waited until the magic blue smoke came, and it was 130°C (266°F), wait for it:
Of course, we don't want to burn people so we looked if we could measure the resistance variation with heat.
The measures are fairly inaccurate as we used a thermal camera, but the graph below gives an idea of how this Resistance VS Temperature behaves:
If we can ensure that there is no humidity (sweat, rain, etc), it seems realistic to use the resistance measures to estimate the temperature and stop heating above a threshold (ex: 74 ohms <=> 50°C / 122°F).