The Debate About Fiberglass Versus PPO/PA Plastic Motorcycle Saddlebags

Hey, when I published an article about Sinister Industries and its PPO/PA plastic material 4″ extended saddlebags, some wondered about the material used on their own stock and after-market motorcycle bags, and others in the industry producing fiberglass bags were not to happy that I ‘advertised” PPO/PA plastic.

First let me mention again that Harley-Davidson abandoned fiberglass about 5 years ago and that all their saddlebags are now made out of PPO/PA. So, for those who want to know more and compare (I had to receive a full briefing). Advantages of PPO Plastic include: High strength, High heat distortion resistance, Outstanding hydrolytic stability, Good creep resistance, Resistance to stress cracking, Resistance to weathering, Excellent chemical resistance, No body work needed, Super light weight, Inside lining not required. Disadvantages of Fiberglass include: Heavy, Stress cracks over time, Inconsistent thickness, Air bubbles, Requires body work, Inside needs to be lined. (yes, picture is my own Harley Road King…still with fiberglass bags)

8 Responses to “The Debate About Fiberglass Versus PPO/PA Plastic Motorcycle Saddlebags”

  1. 1 Jeremy May 19th, 2010 at 2:52 pm

    Nice bike, bags, pic, Cyril.

  2. 2 Woody May 19th, 2010 at 3:30 pm

    FWIW, fiberglass bags don’t have to be lined if made by the RTM method.
    I take it from the article that fiberglass bags have NO advantages and PPO/PA bags have NO disadvantages? Just curious since I’ve never worked with PPO/PA. Thanks.

  3. 3 Seven May 20th, 2010 at 12:30 am

    Quality and well made GRP ( Glass Reinforced Plactic or “fiberglass”) doesn’t need to have any of these issues “Heavy, Stress cracks over time, Inconsistent thickness, Air bubbles, Requires body work, Inside needs to be lined.” at all. Those comments are just the usual scaremongering negativity sprouted by those who use other materials on their products.

    GRP is heavier than PPO though. On a 650lb plus bagger 10lb more isn’t going to make much difference though. Not a lot can be done about that.

    There are lots of cheap and poor quality GRP products out there that do sometimes have these issues though, but suggesting all of them do is bordering on dishonest.

    Biggest advantage of GRP is it is economical to do low volume production runs and is very repairable if damaged. You can modify it too without any major issues. PPO is massively cheaper than GRP for large production runs. Why its use is so common on production vehicles.

    PPO is AFAIK almost impossible to repair if cracked or damaged and nothing will bond to it well, If damaged at all you will need to buy a replacement part from the manufacturer if they are still in business or making that part then.

    Both products have their place in the market place. Neither are without failings.

    Come on, Cyril, balanced and fair articles please. This one wasn’t.


  4. 4 Joe Mielke May 20th, 2010 at 7:56 am

    There really is no debate to be had. Either the part is quality construction and fits properly or it does not.

  5. 5 KG May 24th, 2010 at 11:08 am

    Check out SMC, it is now used by almost all automotive manufacturers, and including H-D on the VRSCF. This is a fiberglass that has many of the advantages of plastic more rigidity and is repairable like fiberglass. The only real disadvantage is that, it does cost slightly more per part. H-D used to make some of there parts this way, but invested into plastic tooling right before the automotive industry perfected the product to be a class-A surface with no prep required.

    Being a builder yourself Cyril, I think you would be interested in the use of this product as structure, it can even be done with carbon.

    Some of the cars SMC is used on

    MBZ: most all of there hard top convertibles
    Toyota: there entire truck bed
    Chevrolet: most of the Corvette

    I enjoy your blog and keep up the good work,


  6. 6 bean're May 27th, 2010 at 11:16 pm

    Its about time for a new set of bags for my chopped roadking since winning the last scotter tramp triathalon with cycle source but I got a few MORE crackss in the bags now. I’d be interested in testing a set. My old fiberglass bags have over 240,000 miles on them but fortunatly only a handful of real accidents.

  7. 7 ROACH Jun 9th, 2011 at 3:35 pm

    If proper fiberglass & ISO or Poly Resins are used (unlike what Harley used) PPO/PA cant even come close to its strength & light weight quality that fiberglass can achieve… PERIOD …. Only Carbon fiber is stronger…. PPO/PA is way down the strength chain but still much better then what SMC and GBA fiberglass that Harley used on their parts….. Harley was about saving money and using the stuff most bottom feeders use..PERIOD! …. 40 years Composites ITT. NASA, WESTINGHOUSE, LOCKHEED trained & certified. Smoke can be blown only so far before its seen by those who know the REAL DEAL!

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