When working with Layer Masks, the Properties panel can be used to non-destructively soften the edge of the mask enabling it to be re-edited at a later time. This can be very useful if the size of the original file or even layer needs to be changed in the editing process.
To add a non-destructive feather, select the desired layer mask on the Layers panel. Then, on the Properties panel, adjust the Feather slider as needed. Although this feature was in Photoshop CS5 (via the Masks panel), in Photoshop CS6 the Feather values support decimal places.
Note: in Photoshop CS6, the Marquee, and Lasso tool’s feather values (in the Options bar), support decimal places as well.

Hello Julie,
I love your tutorials; your are the best! I could watch your tutorials all day.
I would like to know, after cropping an image, how to add a different background, and then ‘feather’ the edges to ensure the image looks as though it is part of the newly applied background pattern — not as though it was just cropped and pasted.
Thanks in advance for any advice you can provide.
Hi:
After selecting a layer, when I go to the Properties Panel, I get the message, “No Properties.” How do I get the Feather slider?
The feather slider is available when you have a mask selected.