Periodically I like to post little tidbits about needlepoint techniques, threads, materials, etc.  While most of us may know this information,  I find it never hurts to refresh my memory and I hope there are many folks out there eager to learn more about needlepoint!  The following is an excerpt from Wikipedia about the materials used for needlepoint:

Materials

The threads used for stitching may be wool, silk, cotton or combinations, such as wool-silk blend. Variety fibers may also be used, such as metallic cord, metallic braid, ribbon, or raffia. Stitches may be plain, covering just one thread intersection with a single orientation, or fancy, such as in bargello or other counted-thread stitches. Plain stitches, known as tent stitches, may be worked as basketweave, continental or half cross. Basketweave uses the most wool, but does not distort the rectangular mesh and makes for the best-wearing piece.

Several types of embroidery canvas are available: single thread and double thread embroidery canvas are open even-weave meshes, with large spaces or holes to allow heavy threads to pass through without fraying. Canvas is sized by mesh sizes, or thread count per inch. Sizes vary from 5 threads per inch to 24 threads per inch; popular mesh sizes are 10, 12, 14, 18, and 24 (Congress Cloth). The different types of needlepoint canvas available on the market are mono, penelope, interlock, rug and plastic

• Mono canvas comes in the widest variety of colors (especially on 18 mesh) and is plain woven, with one weft thread going over and under one warp thread. This canvas has the most possibilities for manipulation and open canvas. It is generally used for hand-painted canvases.
• Penelope canvas has two threads closely grouped together in both warp and weft. Because these threads can be split apart, penelope sizes are often expressed with two numbers, such as 10/20.
• Interlock Mono Canvas is the more expensive because it is more stable than the others and is made by twisting two thin threads around each other for the lengthwise thread and “locking” them into a single crosswise thread. Interlock canvas is generally used for printed canvases. Silk gauze is a form of interlock canvas, which is sold in small frames for petit-point work. Silk gauze most often comes in 32, 40 or 48 count, although some 18 count is available and 64, 128 and other counts are used for miniature work.
• Rug canvas is a mesh of strong cotton threads, twisting two threads around each other lengthwise forms the mesh and locking them around a crosswise thread made the same way; this cannot be separated. Canvases come in different gauges, and rug canvas is 3.3 mesh and 5 mesh, which is better for more detailed work.
• Plastic Canvas is a stiff canvas that is generally used for smaller projects and is sold as “pre-cut pieces” rather than by the yard. Plastic canvas is an excellent choice for beginners who want to practice different stitches.