Saltwater fly reels come in two formats: sealed disk drags, requiring some maintenance, and cork drags, requiring a little more. Cork drags are almost all found on draw-bar reels, which are used for big-game fishing. The most notable examples are made by Tibor and Abel—all pricey, high-performance models. Sealed disk drags are found on everything else. Nautilus, Orvis, Sage, Ross, Lamson and other companies use sealed disk drags. If you don’t know what kind of drag your reel has, it’s probably a sealed system.
With a draw-bar reel, tension is increased by twisting the tension nut (the big adjustable drag handle), thus pulling the spool-side of the reel tighter against the brake surface, which is mounted on the frame side. A one-way clutch mechanism allows the spool to turn freely in one direction, but it drags against the brake surface in the other, thus creating fish-slowing drag. By increasing the tension, you draw or pull the cork drag surface under greater pressure, increasing drag. Cork-based draw-bar reels have two very large braking surfaces, making them great at slowing fish, but difficult to fully seal. Often, the cork is visible when you dismount the spool.
Sealed drags, meanwhile, are usually of the stacked-washer design, in which multiple small washer-shaped brake surfaces are “stacked” in a horizontal column inside the large arbor, thereby allowing the drag washers to be fully protected from the elements. Stacked washers achieve braking by having multiple small surfaces sliding against each other, instead of one single set of brake pads. These washers are usually alternating layers of pancaked metal and Delrin (a type of slippery plastic). Since they are inorganic, they don’t require lubrication once the system is sealed at the factory. (Some reel manufacturers, most notably Lamson, cram a larger drag area into a smaller arbor space using sophisticated 3-D architecture instead of stacked washers, but the core principle of metal sliding against Delrin is still in force).
Both drag types have their proponents. For protecting the lightest tippet for a given species (think line-class record fishing), cork has a slight advantage due to its lower start up inertia. Due to its organic nature and lateral flexibility, the cork drag surface builds up to maximum braking power over a short period of time, as the cork compresses sideways instead of fully engaging at max power the second the tippet comes taut. That can protect the tippet on a hot fish. The tradeoff with cork drag reels, however, is they are a bit less foolproof—and the value of cork has become almost academic, now that synthetic sealed drags have become nearly equivalent in terms of their startup inertia.
What happens if water or sand gets between the drag surfaces of an unsealed reel? Drag failure! Getting water inside an unsealed drag can cause the brake surfaces to hydroplane just like tires on wet asphalt. Sand, meanwhile, can chew up not just the drag surface but also the spindle, the locking gears that hold the spool on, and even the drag engagement clutch. Suddenly losing drag pressure on a hot tarpon or permit can cause catastrophic reel failure. At best, you’ll have a nasty backlash and snarled line to pick out. At worst, the reel may free-spool as the fish steals line, endangering the guts of the reel altogether.