Crystal Cards are crucial for analyzing snowpack-structure as the difference between a weak layer and a well-bonded layer doesn&';t look a whole lot different to the naked eye. Crystals placed on the cards, however, become instantly recognizable and sizable. The BCA cards are available in two options, Polycarbonate and Aluminum. The polycarbonate version doesn&';t absorb as much solar radiation, meaning you can analyze crystals longer before they melt in the sun. The Aluminum version is a bit more durable. The BCA Crystal cards can also be used as tiny plates when winter camping or as throwing stars when attacked by bears. Comes marked with both 1mm and 3mm grids for scale.