I previously tested this machine by sewing a medium 4mm weight leather. It handled it so easily I figured I would try out some heavier leather (3mm thick) I had in my stock pile. I was reading reviews on Amazon when I created this video. Several said this machine wasn't heavy duty at all; that is was all plastic, etc... While the cover is plastic the frame is all metal. That is what is important as it keeps everything in alignment. For the price of this machine (seen on Amazon for as little as $139) this is indeed a Heavy Duty Machine for the very affordable price point for the home market sewer. Yes, more expensive machines may be able to do the same or even better, but not at this low price point. I have machines that will sew through very dense and thick materials, but they cost 10 times what this little machine does. I also have machines that cost 3 times this that won't sew through thick materials with the ease that this machine does. Another option for sewing heavier materials (leather, jeans, canvas, etc...) is an old vintage machine you can often pick up at thrift stores. These are the machines that are solid metal and have external motors that can easily be replaced and upgraded to a 1.5 amp motor for around $70. The point of these videos is to help those of you considering this machine make an informed decision.