Some other tools you may want to consider. The standard utility knives that we all use are dulled very quickly by the fiberglass. Hence I have switched to the "Stanley pocket knife. It has a longer, heavier, replacable blade.

http://www.amazon.com/Stanley-10-049-Pocket-Knife-Rotating/dp/B00002X201/ref=sr_1_1?ie=UTF8&qid=1392740389&sr=8-1&keywords=stanley+pocket+knife

I have found that this sharpener is the fastest way to put a usable edge on the above knife. I would not want to use it to sharpen carving knives but for the Stanley or for kitchen knives it is great.

http://www.amazon.com/gp/product/B00032S02K/ref=oh_details_o08_s00_i01?ie=UTF8&psc=1