Glass

 is a craft-able crafting resource that can be made using any furnace currently available. It has a wide variety of applications, including certain constructs, as well as being the first step towards making more advanced glass receptacles.

Recipe
Note; as one upgrades their furnace, glass production becomes less efficient overall. While the Product:Time ratio increases (more product produced in the same amount of time), the Product:Material ratio decreases (more mats and fuel for relatively less product). From Furnace -> Furnace 2, the yield increases by 50%, but the required materials and fuel increase by 100% and 66%, respectively. From Furnace 2 -> Furnace 3, the yield increases by 33%, but the required materials and fuel increase by ~50% and 60%, respectively. In addition, the Product:Techpoint ratio also decreases (less techpoints per product). In summary, from Furnace -> Furnace 3, the product yield is doubled in the same amount of time, but the material and fuel costs are tripled and the techpoints are halved.