Foil kites rely on the wind to fill cells in the kite to form their wing, they have no hard structures. The top canopy is connected to the lower canopy with cloth ribs to form the cells. The wind plays a huge role in inflating and keeping the shape of the kite.
Foil kites are used for kite racing and advanced recreational kitesurfing. They do not have any flotation.
Foil kites require different skills to use them safely and have some different control and safety mechanisms to inflatable kites.
Foil kites are used for recreational kitesurfing (particularly for light winds) and for racing in combination with foil boards
Closed cell vs. open cell foil kites
Closed cell and open cell foil kites share a bridle system and have a similar internal structure created with the cloth battens that hold the top canopy to the lower canopy.
The difference between an open and closed cell foil is whether or not the leading edge of the kite is open so you can see the individual cells of the kite.
A closed cell foil has the front of the kite closed off and has a series of baffle ports that allow air into the kite. When the kite is leading edge down in the water the baffle ports are closed off on the inside of the kite with flaps of fabric. This allows the foil kite to be relaunched off of the water. They are commonly used for kitesurfing.
A open cell foil kite has openings on the front of the kite. These will fill the kite with water when it is crashed. They can also be "over-inflated" with excess pressure when gusts are encountered then partially collapse when the gust dissipates. They are commonly used for snowboarding and landboarding.
Advantages of foil kites
Very good for light wind conditions
Very good upwind capability
Fast kite speed
Stable and predictable in the air
Compact (packed) compared to an inflatable kite of the same power
Easy for a novice person to assist with landing (given appropriate instructions)
No pump is required
Generate more power than inflatable kites (e.g. a 10m foil can have same power as 14m inflatable)
Quick to launch (if no tangles)
Disadvantages of foil kites
Complex bridle system that can get tangled
No flotation - the kite can sink if it is crashed onto water (don't crash it!). Closed cell foil kites do float for a while.
Some older models can be difficult to use - e.g. wingtips fold
Less durable than an inflatable kite - more prone to damage from hard crashes
Check lines and bridle carefully before launching - remove knots and line inversions
Line extensions can provide more power in lighter winds
Pre-inflate the foil kite cells prior to launching
Launching and landing
Use a hot launch (kite downwind) in low wind
Use a side launch (45 degree angle to kite) in stronger wind
Use side landings in anything above light wind
Practice water relaunches, including leading edge down (use steering lines to flip kite over)
Flying a foil kite
Sheet the bar out to generate power - do not dive the kite like you do with an inflatable kite!
Keep the kite in the power zone in turbulent wind to avoid it overflying.
Partly Trim (de-power) kite in light winds.
Avoid fully sheeting in the bar - this will backstall the kite
A race bar has a much larger depower range compared to a standard bar for some kite models (e.g. Ozone Cronos and R1)
Maintenance and safety
Check line lengths regularly - do a thorough check after 60 hours use
Wear a buoyancy vest
Don't use a foil kite in surf
Never the fly the kite overhead at 12:00 on land
Self rescue procedure
Get to your board first and straddle it, then wind in your lines
Pack the kite down (see video)
Wrap and secure it in your harness
Place your kite and harness on the board.
Push the board in front of you and kick/swim to shore
Closed Vs Open Cell Foil Kites for Kiteboarding and Snow Kiting, Mackiteboarding.com
Don't Fear The Foil Kite, IKSURFMAG