Heated Shoe Insole/Heating Foot Warmer/Boot warmer/Bootwarmer - soft, comfortable heating foot warmers insole is contoured to the shape of your foot without interfering with the fit of your shoe or boot. Fits right inside your shoe with guided trimming lines. One size fits all foot warmers are perfect for those cold football Sunday afternoons, will fit over nordic, snowboard, snowmobile, timberline-like, horseback riding/paddock, hiking and work boots and more. Heated Shoe Insole or Heating Bootwarmer is powered by 2 sets of AA NI-MH battery packs,1 set of Ni-MH battery pack per insole. Battery pack casing can be securely attach to calf or ankle. And may be worn inside or outside of pant leg. Used like an insole, place heated insole between socks and inside of shoe or boot. Cozy insoles reach a temperature just below that of body temperature, approx.98 degrees Fahrenheit or 36 ~ 37 degree Celsius. Heated insoles is intended to take the chill off, so it's not realistic to expect strikingly noticeable heat - they won't make feet become hot. Rather they maintain a temperature of an approximate body heat of 98 degrees Fahrenheit or 36 ~ 37 degree Celsius, so when normal blood flow won't keep toes warm, heated insoles will make up the difference keeping feet warm when you need it. Each set of battery pack is estimated to keep feet warm for 9 hours. Long lasting, it won't lose effectiveness like microwaveable or reactive chemical heating elements, ideal for diabetics and other persons suffering from poor circulation thus cold extremities Advantage of Ni-MH Batteries With the development of new nickel-metal hydride (Ni-MH) battery options, improvements in electronics have now been matched by significant improvements in the batteries that power them. Nickel-metal hydride battery cells provide more power (in equivalently sized packages) than nickel-cadmium (Ni-Cd) cells while also eliminating some of the concerns over use of heavy metals in the cells. Safety These insoles are extremely safe. Low amperage eliminates all possibility of shock or burn, even when wet. Certification(s): CE UL