The Suction Seal
In order to get a swim goggle to fit, there must be a tight seal between the eyecup and the face. There are two ways of accomplishing that: Suction or Positive Pressure.
With a suction seal goggle, the goggle shape must allow the sponge or flange to be pushed into the skin. Then the basic suction principle takes over. Since a suction goggle only matches the face partially, the facial tissue must be pulled to the goggle to complete the seal.
The facial tissue is attracted to the goggle with negative pressure, suction. There is very little tissue to move near the inner corner of the eye (1), so if the goggle doesn't match fairly closely with the general eye socket shape at this point is won't develop a suction. This general description of the eye socket has been described by some as round, or oval. If the area has a narrow, rather acute angle around the inner corner of the eye, it's described as oval. If the angle is broad it is generally described as round. After checking this area the goggle frame has to be wide enough to cover the separation outside the outer corner (3).
At this point, a soft sponge or flange must must least be close to the skin all around the periphery of the goggle, By compressing the sponge and pushing in on the frame, air is pushed from beneath the goggle creating the necessary negative pressure to keep the tissue pulled against the frame.
This is why coaches have told swimmers for years that for a goggle to work it has to stick to their face with suction.
For a long lasting seal the sponge must be pulled at least 1/8 inch or more into the tissue, Otherwise the seal tends to break each time the swimmer takes a breath, because the shape of the tissue changes. This long lasting seal also leaves the red rings, and occasional swelling around the eyes by limiting blood flow and lymphatic return around the eyes. This effect can be pretty long lasting too.
Even with suction goggles the shape of the frame determines fit!
Barracuda has searched the world for the best fitting, most comfortable suction seal goggles, and offer them as their Barracuda Suctions Seal swim goggles.
Nosebridge adjustments re less precise on suction seal goggles and, some like the Electra, Convertible and the Predator have a fixed nose bride for convenience.
Overall frame size is more critical on suction seal goggles , because of the areas at the inner and outer corners of the eyes (1 and 3). If a goggle is too large it tends to lose the suction seal at the outer area of the eye and temporal area, especially while taking a breath. If the frame is too broad, or "tall" it won't fit into the inner corner of the eye closely enough to cause a suction. Too small a frame either wont seal at all, or impinges on the field of vision. Goggles meant for small face sizes are often referred to as "juniors". The Frenzy and Psychedelic are such goggles.
The Positive Pressure Seal
The Positive Pressure, or anatomical seal, works on a different principle. Frames on The Positive Pressure goggles are shaped all around the eye to more closely match the tissues they rest on. In addition, at each area, the frame matches the underlying bone structure. This directs the foam into those areas which are more difficult to seal, especially the three areas shown in the picture.
At the corner of the eye (area 1) the frames pushes the sponge against the side of the nose, and into the depression which often occurs across the top of the bridge of the nose. The frame pushes foam into the depression between the nose and cheekbone (2). It also allows for the cheekbone by curving in to more closely match and apply less pressure over this area.
At the outer corner of the eye (3), it pushes almost directly back to fill the depression near the outer canthus of the eye. Some swimmers have no marks at any time. The reduced pressure of the frame against the face is also important because it reduces pressure over sinuses and nerves. The pressure on these areas by some goggles leads to pain, and even "goggle migraine".
The size of the goggle is only important in how well it covers the eye, and how much you want to trade a wide field of vision for low drag. The external shape isn't as much about how the goggle seals as it is about how little it will slow you down in the water. Generally speaking, drag from a goggle is directly related to how far it stands out from the face. In other words, how much area there is to resist the water.
Of the Positive Pressure Goggles the standard and the B200 are relatively tall. The B300 and Racer are short, and the Elite and Torpedo, hiding under the eyebrow, are practically invisible. Very hydrodynamic.
Barracuda Positive Pressure goggles more nearly match the anatomy of the face, it is not dependent on suction to create the seal. The sponge acts as a gasket between two like surfaces. A conforming, or "memory" sponge is used to allow for individual differences, without resorting to suction. The critical shape of the goggle is the part of the frame that rests against the face.
The sponge seals out the water by the positive pressure of the strap. The goggle doesn't have to stick to your face to keep out the water! It doesn't leave marks on our face for longer than it takes up heat to dissipate.
