I'd guess Tracy is talking about continuous ridge vent. it is made of plastic and has construction very similar to corrugated cardboard, that is two membranes separated with parallel walls forming channels. plastic yard signs are often made of similar material.
for larger channels and far more rigidity and strength you might consider poly-carbonate. I use it for patio roofs. I know it comes it 6,8,10mm thicknesses. unfortunately, I moved recently and threw out all the drops I had.