What are they like to use?
We fitted both vests to a dummy torso inside a textile jacket on my Yamaha Tracer 700 in a freezer van. We measured the temperature between a windproof base layer and the heated vest at the same point on the chest and upper arm.
We also took readings of the inside of the heating pads over time in the office and photographed each with a thermal camera to see where heat was delivered.
Finally, we went on a road test in a textile jacket with the thermal liner removed, at an ambient temperature of 9°C.
In the freezer
We tested the Keis first and saw 39.4°C on the chest at the end of the test, compared with 4.4°C on the upper arm, in an ambient -3°C. On the Smashnerd vest, we saw the temperature on the chest drop as heating power was increased, with 13.4°C at the chest on full power and 5.2°C at the arm, also at -3°C.
The reason is clear from the thermal images; the Smashnerd had five small pads in the wrong places.
The Keis has three large panels in the right positions for a spread of warmth.
In the office, with each on full power, the Keis was more consistent — no more than 2°C variation over two hours but the Smashnerd varied more — 9.1°C difference over the same period.
On the bike
Powered off, the Smashnerd felt cumbersome and quickly, sweaty and restrictive. After 15 miles, I switched the heating on, at full power to compare with the Keis. The heat was localised and not particularly pleasant. By the time I stopped to swap vests, I was quite uncomfortable.
Putting the Keis on, I barely knew I was wearing it. 15 miles without the heating on, it didn’t feel clammy and when I stopped to activate it, there was no moisture at all. The heating began straight away and after a few moments, settled to an almost-hot sensation that spread exactly where it was needed. Even with the heating on the highest level, I didn’t get sweaty at all.