Bests & Worsts Reviews from Amazon

When I received these, it seemed like only two of the highlighters worked - the others either had no color, or very, very light color. If this happens to you, put the markers in the freezer for a day or so, then thaw them, and they should work! Here's why: the ink in Frixion products is thermochromic; this means that its color hue and/or intensity changes depending on temperature. When exposed to heat (like the heat of a delivery truck during the summer, or the heat created by the friction of the rubber "eraser" on paper) the ink becomes colorless. This transition is reversible - that is, exposure to cold will cause the color to return. Hooray for chemistry! I'm giving this four stars because the thermochromic transition temperature has implications for the use of Frixion products - if you use this highlighter on a textbook you leave on your car's front seat on a sunny day, it's possible (and even probable) that your highlighting will disappear. Granted, you could get it back by popping your textbook in the freezer for a day, but that seems unnecessarily convoluted. Caveat emptor!