@Lilian , if you're getting deep gouges into the mat you are probably pressing down harder then needed. That'll also dull the blades out. Natural fabrics are less dulling then synthetics. That's why
@Lollipop is getting her blades dulled down, cutting nylon netting and lycra.
I use Olfa mats and found I get good results from a Fiskar cutter. Ninety percent of what I cut is quilt cotton, linen or rayon. I can cut several garments and multiple quilts before I need to change blades, but I do not press down hard at all.