Here's a good introduction to the various grades of sailcloth from name brand manufacturers and a link to the specification of the Challenge 6.03 High Modulus cloth that I use for most of my small boat mainsails.  http://www.judybsails.com/v/vspfiles/knowlegebase/Hyde-Sailcloth-Range.pdf http://www.judybsails.com/v/vspfiles/knowlegebase/challengecloth/603challeng... Any weight of woven dacron cloth (of at least 3.8 oz) won't rip easily.  Dacron cloth is incredibly tough,.  It'll loose its shape and become soft as a bedsheet long before it rips from being threadbard.  But weight isn't the measure of quality for sailcloth.  High quality sailcloth is all about being low stretch.   Low stretch means the sail holds the designed shape longer.  The best dacron sailcloth is woven from lower stretch yarns, smaller diameter threads, is more tightly woven, and uses less resin.   All of that costs more, and it's worth it, IMO, if you want your sails to have an almost-like-new shape when they're a couple of years old. Assuming that we're talking about woven dacron, the *brand name* and *grade* of weave is more important than weight.  What is important is the cloth's ability to hold it's shape.  And the quality of construction too.  As the sail ages, will it stretch evenly and uniformly, or will it get lots of wrinkles, and start to flutter along the edges.  There are lots of construction details that only a sailmaker would notice.   For a hank on 128, you could use a 3.8 oz Challenge Performance Cruiser dacron so it flies when a mouse sneezes, as long as you don't use it in higher winds.  that would be the least expensive option using a good cloth.  But if you're going to get a roller furling 128, and intend to use it reefed, then you'd be slightly better off with a less stretchy cloth, like the 5.53 or 6.03 HMD, with reefing reinforcments, etc. (or the equivalent cloth from Dimension Polyant or Contender)  (but in this case the 6.03 HMD cloth is actually less expensive than the 5.53 HMD, because the larger threads mean that the cloth spends less time on the loom) Most importantly, make sure it's name brand cloth if you want it to keep its shape a long time.  Most new sails are a fabulous improvement over old/tired/baggy sails.  The real test is what the shape is like after they've been out in high winds a few days.   Ask the sales person exactly *which* cloth they're building your sail from.  It will have a manufacturer's product code.  Like Challenge 6.03, 5.53 or 3.8 or 7.18, etc.  (BTW, those numbers only roughly approximate the actual weight.  The codes indicate the "grade" of cloth to the sailmaker: what diameter and type of yarn was used to weave the cloth.)  There are many reputable lofts on the internet, all of whom will build you very adequate sails.  You won't go wrong with any of them.  But.....  A final caution: The internet has a few unscrupulous characters selling "knock-offs".  If the sales person from a no-name "production loft"  tries to sell you "6 oz" or can tell you a weight only, ask them for the sailcloth's product code from the manufacturer.  Don't buy until you have a written specification.  There is at least one "internet loft" out there that is using no-name cloth, and claiming they are using name brand cloth.... but if you press them to tell you exactly what cloth it is, they can't.   If you're suspicious, google the loft's name.  When it comes to sailcloth and craftsmanship, you get what you pay for.  Fair winds, Judy B Hyde Sails of Northern California www.judybsails.com   judy@judybsails.com cell: 925.208.1692 fax: 925.820.2327 skype: judith.blumhorst www.HydeSails.com/NorthAmerica   ________________________________ From: Jeffrey Johnston <frjeff@gmail.com> To: montgomery_boats@mailman.xmission.com Sent: Monday, April 2, 2012 9:02 AM Subject: M_Boats: Another Sail Question? I am narrowing it down to a few lofts to order new main and 128 gen. for my M15. Quotes range from a low of $550 to $841. Also, the sailcloth quoted ranges from a low of 4oz to 6.3oz respectively. I have read no real negatives on any of my possible lofts. I am a recreational sailor (day) and may try a few little races with the WWP guys around here. Winds here are Great Lake style (Huron). How critical is sail weight and what does the heavier cloth add to the sail (durability, longer life, just cost, etc?). *Jeff+* Molōn labe!