Why do I make a point of referring to the felt I use as Wool Design Felt instead of just "felt"? Because... there is felt and then there is "my felt". Here is a little explanation.
Craft felts are inexpensive, lofty (think compressible), "pill" easily, wear about as well as flannel and come in a limited color palette. Think bulletin boards in grade school. It can be sewn on a cheap home machine because it is thin and the fibers are not close together in a mat. It will never be in my workshop.
Needle felted cloth is handmade by fiber artists. It is beautiful and allows color manipulation to die for. But it is not durable enough for my bags. Nor is it available in reproducible yardage. Lovely stuff, it just does not meet the criteria needed for my bags. (If someone can make this sturdy enough for my bags, contact me ASAP.)
Industrial felt checks off the durable box, but it is just... not beautiful. It is coarse due to lower quality wool or wool-synthetic blends, all perfectly acceptable in industry (just not ok in a bag). It comes in a color palette of, well... gray and grayer. You won't find the lovely marled colors of Wool Design Felt here. Nor will you see it in my workshop (I tossed the samples.)
Wool Design Felt (aka Industrial Wool Design Felt aka "My felt") is made of fibers from merino and karakul sheep wool that are tightly compressed into a firm felted mat of uniform thickness using a combination of steam and pressure. It is a lovely, expensive material. It is slow to "pill", resists abrasion, is water resistant as well as ecologically sustainable and renewable. It is available in deeply saturated marled colors. It allows me to create high quality, long lasting bags. My favorite day is when I get to wrestle those 6 ft rolls of felt into the studio. Weight training at its best.