Okay. First, you'll want to know if it's full canvas (the best construction). Pinch one layer of fabric from the middle of the sleeve. Rub the pinched fabric between your thumb and and index finger. Feel how thin it is, and the subtle friction when rubbing it together? Now, do this same "pinch" test on the chest, just above the breast pocket (if your hands are dry, I'd recommend licking your fingers so that you can perform the pinch test properly). Rub the pinched layer in between your thumb and index finger. If the fabric is even SLIGHTLY thicker than the fabric at the sleeve was, then your suit is fused. You should also notice a different type of friction if your suit is fused. In a poorly fused suit, you will notice that the fabric is at least three times as thick (but we're dealing in fractions of a milimeter here). If it is a well-fused suit, then sometimes it'll be about twice as thick. Now, if the chest is fused, you can also see if the suit is "half-canvas" -- that is, its lapels are not fused. To test this, rub the front and back of the lapels together. If you feel a "rough" sensation, that's the canvas. If you feel a smooth or stiff sensation, then your lapel is fused. Also, if you aren't sure of whether its fused or not when doing the chest pinch test, you can double check your work by going down to the very bottom edge of the jacket. Do a pinch test there as well. If it jacket is fused, you will feel two layers -- the front fabric and the underside of the fabric. If it is canvased, you will feel a third layer sort of "floating" down there, sandwiched between the front and underside of the fabric.