There are four ways in which Sketch can blur your layers and you can pick between these modes in the header of the blur section.
- Gaussian Blur: This will blur the layer evenly across.
- Motion Blur: Blur only in one direction, giving the illusion of motion.
- Zoom Blur: Blur from one particular point out.
- Background Blur: Blurring the content behind the layer.
The other kinds of blur are kind of self-explanatory, but Background Blur might need a little explanation
Background Blur was added after Apple introduced iOS7 so give designers an easy way to reproduce this effect. To get the right effect, make sure you have a (semi-) transparent fill on the layer, otherwise the blur effect won’t be seen.
Note that blur is a very expensive effect to render - especially background blur - and the bigger the layer and the blur, the more memory and processing power it will take up. Disable blurs if you can, and if you have the choice between using background blur and regular blur, take the latter.