How do you explain about thick fabric to sew?

Of course, it depends somewhat on the type of fabric.

For a home machine, the needle needs to be strong -- say up to size 16 (or 100 in European sizes) or bigger, if you machine can handle it. Not all home machines can accommodate needles larger than 16 (100). For most thick woven fabrics, a SHARP needle, or leather needle might be appropriate. I have never sewn thick, knit fabric, but my serger and home machines, with size 12 (80) universal, ball or stretch needle have handled the load without problem. You can also adjust the pressure on the foot, if necessary, to get a better stitch. To keep layers together on a home machine -- for thick or not so thick fabric -- I almost always use my walking foot attachment. Heavy-duty sewing might be too much for a home machine.

An industrial walking foot machine might be needed for very heavy, thick fabric loads. The presser foot lift, however, can be a limiting factor in the thicknesses it can handle. My two machines can take needles up to size 25, but since they are timed to use size 16 - 22, according to my dealer, I should stick to those needle sizes. I use size 18 and 20 almost exclusively. An industrial walking foot machine can handle heavy, leather fabric layers with ease, keeping the sandwiched layers nicely together. The walking foot is built into the machine mechanism and is not a separate attachment. It is not designed to be used for medium or lighter weight sewing.