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Hunting is primarily a fall and winter activity which has the common element of either being cold part of the day or all day long. Mix in surprise weather conditions like blizzards or rainstorms and you have the conditions for at best a cold hunt and at worst a ripe setting for hypothermia.
Most people think hypothermia, like frostbite on the fingers and toes, requires a dramatic drop in body temperature. In reality the onset of hypothermia can occur with just a few degrees of core body temperature drop. With just a few degrees of temperature drop the body can shiver uncontrollably and speech and thought become distorted. At around 9 degrees of temperature drop (90F core temperature) shivering stops and severe confusion starts, usually resulting in death. The Center for Disease control estimates that roughly 750 people die per year in the U.S. due to hypothermia, the majority of which occur during the fall and winter. CDC case reports.
Combating hypothermia is simple; stay warm and stay dry. Staying dry means bringing along an extra change of clothes if you get wet, staying warm can be more challenging though. To help with the challenge of staying warm, Tech Trade LLC, makes a line of Ready-Heat™ vests and blankets. For this review we decided to take a look at Ready-Heat™'s heated disposable vest. The disposable vest was originally designed for combat medics and EMT staff to stay warm while working in inclement weather. Recently these types of products are becoming more available to hunters and outdoor enthusiasts.
The vest is a one-time-use cloth shirt that you put on before heading out in the field or carry along in its vacuum pack in case of emergency. The vest secures with velcro like strips on each side. Unfortunately the strips tend to dangle on an average size person and can get in the way. A simple solution is to clip or cut the loose portions of the strips once you have put the vest on. On the plus side, Tech Trade has made the strips long enough to still fit a person that wears XXXL sizes.
In our tests, the vest warmed up quickly, starting to produce heat within 2 minutes of breaking the vacuum sealed package. Within 10 minutes it had come up to a steady state temperature of around 100F, which is slightly higher than the average persons body temperature of 98.6F. For our testing the vest was worn over a light t-shirt, then a long sleeve shirt and heavy winter coat were worn over the heat vest. The vest produces a comfortable level of heat while at rest. However if you are in motion you may begin to sweat depending on your physiology, what you are wearing, and the temperature outside. If you start to sweat, peel off a layer of clothes. While the vest is water resistant and will continue to operate, you don't want to start perspiring in the cold since this will wick more heat away from your body.
Surprisingly the vest was still producing heat after 14 hours, although we noticed a drop off in heat production after 10 hours. This is surprising because the package states up to 8 hours. Your results will vary depending on the amount of oxygen available to the heat packs. Wearing the vest under several layers of cloth will reduce the oxygen flow and make the vest last longer. Letting it run uncovered with nothing around the heat packs will allow it to run hotter but for a shorter overall duration. Note that, because of the heat produced, you should not wear the vest directly on your bare skin, rather wear it over a light shirt and then put your other clothing layers over the heat vest.
The vest has six heat packs total, two heat packs on the front; one for each lung. The front two packs are in a good place to easily tuck your hand into your armpits and use the packs to both warm your hands and chest.
The remaining four packs are placed in a quadrant of the lower back region. The idea behind placing the majority of the packs on the lower back is because this rides near your kidneys and warms the blood coming to and from your lower extremities.
One may be concerned that the chemical process used to produce heat is toxic or dangerous. While the package specifically states not to wear the vest while sleeping, the chemistry involved is safe. The reaction is an oxidative process that is similar to but not nearly as explosive as combustion. The main ingredients are iron, wood powder, carbon, vermiculite, and oxygen from the air. Basically once the heat packs are exposed to air, the iron is oxidized producing heat, rust, and water. The wood powder, carbon, and salt serve to speed up the reaction and the vermiculite absorbs the water reproduced. Over the course of time the heat packs become more rigid and take on a small bit of weight, neither of which is noticeable unless you are paying attention.
 The sealed vest pack weighs 10 ounces and measures 7"x10". This makes it ideal for throwing in a backpack since it takes up a minimal amount of weight and space. Shelf life is 3 years so you don't have to use the vest in one season, although you might want to write the date you purchased the vest on the package, since the packaging does not have a manufacturing date.
If you solely want to use the vest for survival purposes, you may also want to consider Ready-Heat™'s heated blankets (http://www.Ready-Heat.com). While we did not review them, they offer more heat production and a longer run time at a slightly higher cost and weight. Conceivably both the vest and the blanket would be the best combo in the event of an emergency. At the least the heated disposable vest can help make your cold hunt warmer and at the most it could help you get through the cold of an emergency or survival situation.
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