Quilted Warmers

Not overjoyed at the prospect of starting the day on a seat frozen overnight? The simplest way out, it would seem, is to buy an electrically heated cape. However, having put nine such "quilted warmers" through a lab test, we became convinced: not every one of them will provide a warm spot.

Two things concern the motorist: how it heats and how much it charges for it (in rubles and in watts). It would seem that since all the electric power fed into the heater turns into heat (there is nowhere else for it to go), one could jump to the hasty conclusion: more current - more degrees. But that is only at first glance. Remember: water at 100°C will scald you instantly, whereas the heat of air heated to the same temperature (in a banya, for instance) is borne quite easily. In just the same way, in hard frost your tongue may freeze to metal, yet it will not even feel the cold of a piece of foam plastic.

It all comes down to the thermal conductivity of the material. If it is low, then at the point of contact with the body the temperature will hardly differ from 36.6°C! Such a material is good for a "passive" pad - it will keep you from feeling the cold of the seat, but it will not warm your backside either. But in the case of a built-in heater, this same material will hold back the flow of heat from the coil to the surface. So what is needed is high thermal conductivity? But then measures must be taken against overheating during the heater's prolonged operation, otherwise a burn will not be far off!

We had to organize a rather elaborate laboratory check of the capes' thermal conductivity. This is done with a calorimeter. First the item is heated in a special chamber to a set temperature, and then the rate at which it cools down is measured. The result is the thermal conductivity or, as in our case, the value of the total thermal resistance. The greater it is, the lower the thermal conductivity, and vice versa.

But how do you compile a rating when what matters is the outcome of the "contest" between power and thermal resistance, not each parameter on its own? We decided to divide the first quantity by the second and obtain a certain conventional figure that says how quickly you will feel the blissful warmth. More points - the sooner the real onset of the effect. Naturally, when choosing in a store, everyone can refine our formal assessment by taking into account the price and a number of additional merits and drawbacks, which we listed in the photo captions. It would not hurt, for example, to look at the fastening straps - whether they suit your seats (not all cars have extendable headrests) and whether they allow the cape to be taken off and put back quickly if, say, the family has a couple of cars. If the cigarette lighter socket is live at all times, an auto-shutoff function will come in handy.

Note this: two of the items, besides the heaters, also have little electric massager motors (they consume very little - just 1.5-3 W)! They say it is good for you. We did not check. But do not count on extra heat from friction - the motors are surprisingly frugal. As for heating, the cape with three massagers is in bad shape: the built-in heater's power is too modest - just 6.6 W - and it warms only the small of the back.

Aleksey Vorobyov-Obukhov