What is Isinglass? Does it exist? In the minds of most mariners, Isinglass is very real. It’s the clear plastic window material in their boat's canvas enclosure. And they know that it’s expensive to replace when it becomes cloudy, charred or cracked. But what is it? The dictionary is of little help: [Isinglass-1: a transparent, almost pure gelatin prepared from the air bladder of the sturgeon and certain other fish and used as an adhesive and a clarifying agent. 2: mica, especially when in thin transparent sheets.]
This material was commonly used in the old days as heat resistant windows in stove doors.
So how did isinglass jump from fish guts to our boat’s windows?
Clever marketing may be the answer. Isinglass [or Eisenglass] was the brand name for a product that has not been manufactured in 40 years. It’s a term who’s common usage has lingered in the maritime vocabulary for decades and who’s meaning has evolved from brand name to noun-as Jello is actually a brand of gelatin. There is much debate and speculation among boaters about what eisenglass [or isinglass] really is. Most experienced boaters think it only refers to the clear vinyl sheets such as Strataglass. Some think it's sheet vinyl and roll vinyl. Others think it’s also polycarbonate and lexan. With all these competing variations of a word that dosn't really exist, perhaps we boaters should demand to include our mysterious term in the dictionary and settle this once and for all. How about: Isinglass- A clear material commonly used for windows in marine enclosures.
So now the question is: What kind of eisenglass should I install on my boat?
There are several different types of window materials on the market to suit our various needs:
*Double polished roll vinyl. This is the stuff in use on about 80% of the boats. It's not quite as clear as sheet vinyl but is more flexible for rolling up.
*Extruded roll vinyl. This is the same material but the manufacturing process is different.
*Press polished sheet vinyl. Has more clarity than the above two. It's especially good if the panels stay up all season since it is stiffer and does not roll as tight. This is the stuff that the boater who knows it all will insist is eisenglass.
*Sheet vinyl with a protective coating. Available as the brand Strataglass. All of the above window materials are made of the same thing-PVC. Strataglass has an additional scratch resistant coating.
*Polycarbonate. Will not roll up. This is by far the clearest product available and is mostly on large boats and yachts.
*Lexan. Usually never on canvas. Used primarily for windows in the hull and hatch covers.
The important and expensive decision of which window material to install depends entirely on how one uses their boat and it’s canvas. Just because sheet vinyl costs more than roll stock and offers more clarity doesn’t mean that it’s better. Not if the windows are removed often and must be rolled up tightly to stow in a small space. Sheets need to be stored flat or rolled very loose and big to avoid cracking them and are better suited for enclosures that stay up all season. And if visual clarity is most important, polycarbonate is actually clearer than glass! And priced accordingly.The best way to determine what kind of isinglass suits your needs is to consult your local marine canvas professional. While the debate about the existence and proper use of the term- isinglass rages on, it's stubborn endurance in the maritime lexicon is a testament to the importance of clear vinyl windows in marine applications.