The new jars are made from durable, high temperature plastic that can withstand the heat and pressure of an autoclave making them virtually indestructible, and perfect for mycology use. These jars are also slightly larger than the regular half pint wide mouth jars previously used; this means approximately two ounces more substrate is inlcuded in each jar! The substrate inside is made with only the freshest and most organic grains available. Video on how to use Mushbox Substrate Jars