Thermo-form Sheet and the Line of Extrusion

Most thermo-formable sheet stock, including Kydex, is extruded into its final thickness and texture.  This process creates a “grain” to the material, similar to wood.  You can see this “grain” direction by reflecting light off the back or un-textured side of the sheet.  You’ll see faint lines running parallel to the direction the material was extruded.  You can also detect the grain direction by looking carefully at the texture of the material.  Here is a picture trying to show the grain direction by painting the material with reflective paint.  You can see how the light reflects differently off of the texture depending on which direction the grain is going.

This is important to know for three main reasons:

·         First, the material will shrink (contract when heated) much more along this line than across it.  You could cut a 6”x6” square and after heating it will measure about 6”x5.75” so keeping the grain in mind while cutting raw material is important.  The shrink rate can vary from batch to batch of material and from color to color.

·         Second, the grain will affect the retention of your finished holster, sheath, etc.  The material will flex more along the grain than across it.  Items formed with the grain perpendicular to the draw direction will have comparably more retention than items formed with the grain parallel to the draw direction. 

·         Third, repeated stress on the material can eventually cause stress fractures in the material.  These fractures will tend to travel along the grain of the material more easily than across the grain.  Identifying the most likely stress points on your projects and orienting the grain to minimize the chances of material failure will improve the long-term durability of your projects and products.  This is critical when constructing belt loops with your Kydex.  If the loop is made with the grain parallel to the long axis of the loop it will last quite a bit longer than loops made with the grain perpendicular to the loop.

So there you have it, keep the grain direction in mind as you make your projects and you’ll be happy with the results when you do it yourself!