We put the hand warmers inside a couple of medium-dark colored Patagonia fleece jackets, hung them out in the weather, and took temperatures. The Grabber Mycoal did best there, as well as in our human-hand experiments.

Quite a few of us are in the boatyard at the first hint of spring, even if the frost has not turned to dew. There's prepping and commissioning, and the motorsail to the marina. But, pushing the envelope often means standing in pools of cold water with wet feet and hands while sanding a bottom, or taking a shift at the tiller wearing multiple layers of fleece and heavy gloves.

As invigorating as these activities are, they are less fun when our extremities—hands, feet, and ears— are cold. Enter the pocket-sized hand, toe and body warmers. We've learned on chilly days that these pouches can convert stiff fingers and toes to…