Features:
The SFF21D is the 800RPM model. Even with a lower RPM, this fan still manages to move a pretty decent 33CFM of air. The impressive part is that this fan is rated at only 8.7dBA, so ideally you should barely be able to hear this fan in operation, or not at all.

 
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Next, we have the SFF21E S-Flex fan. This is the 1200RPM model which is rated to move 49.0CFM of air while running at around 20.1dBA. This is probably going to be the more popular fan for users looking for performance vs. noise ratio because it offers great airflow for cooling a PC case or CPU cooler, but still remains relatively quiet and unnoticeable while in operation.

 
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For users looking for a little more serious performance at the cost of using a slightly louder-than-silent fan, then the SFF21F is what you're after. This fan runs at 1600RPM and moves 63.7CFM of air at a noise level of 28.0dBA.

 
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Using Sony's Fluid Dynamic Bearing technology, these fans have a rated lifespan of approximately 150,000 hours in operation! To put this into comparison, your average sleeve bearing fan has a MTBF (mean time before failure) rating of 20,000 hours, ball bearing fans average about 50,000 hours. So as you can tell, 150,000hrs is very impressive for these fans. This bearing design also has an increased anti-shock ability, making the bearings up to 5x stronger compared to conventional ball bearings.

Measuring 120x120x25mm, the S-Flex fans are your standard 120mm fan size and will easily fit in any case or cooler mount.

The power cables on each fan are all 30cm long with a 3-pin power connector at the end. If you don't have a 3-pin fan header available, or your motherboard can't supply enough power to drive these fans, then Scythe has included a 3-pin to 4-pin molex power adapter with each fan. This adapter also has an RPM monitoring lead which you can plug into either your motherboard or a fan controller to monitor the fan's RPM.