I purchased some Sigma brushes about a month ago and decided to add my opinion to the other opinions floating around in the blogosphere.
First, I have to hands down give Sigma koodos  for their customer service. I purchased a brush when the company first  came to my attention about two years ago. Later on the brush head came  loose from the handle. It turned me off the whole company. When making  an order for my new brushes I mentioned my past experience. Sigma kindly  enough sent me a brand new replacement of the brush that was damaged. I  was blown away by how easy it was. They are a company that definitely  is set out to make their customers happy.
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| Brand new F50 replacement brush. | 
Sigma has come out with a line of three brushes called the Sigmax HD  line. The collection consists of three synthetic brushes that you can  buy individually or in a set.
Sigma has been compared to MAC  brushes quite frequently. But these new brushes have no MAC comparison  and are in my opinion amazing quality. In fact the F82- Round Top  Kabuki  has replaced my 
MAC 109 for applying/buffing foundation.
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| Sigma F82- Round Top Kabuki | 
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Price:  
16$
Use:
 I use this brush to buff in foundation and concealer. It is small enough to fit around the nose and under the eyes.
This brush creates flawless/realistic looking skin. It is perfect for cream and liquid foundation.
It  can also be used to buff in cream blush to create a seamless  application. No one wants to leave the house looking like a clown!
Note:
If  you have dry skin, be careful not to over buff because it will only  emphasizes dry patches on your skin. Make sure to moisturize well and  this will be your best friend :)
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| F80- Flat Top Kabuki | 
Price:
16$
Use:
I  currently use this brush on my powder foundation days. I use a pressed  powder and this brush allows for adequate coverage which can be hard to  achieve with a powder foundation.
Note:
You  can use any brush for whatever you want! The MAC 109 is not a  foundation brush, it is advertised as a contour brush. The same goes  with these brushes. Use them as you please to create you own desired  looks.
Overall: 
 Quite Simply, these brushes retail at a  great price in comparison to other higher-end companies. The quality far  surpasses the price. There is another brush in the Sigmax brush line that I do not own. 
Remember  ladies, brushes are your tools to achieve beautiful make-up looks,  great tools make great looks. Invest in quality and I guarantee you will  notice a difference! Keep 'em clean by using a mild baby shampoo once a  week.
I may do an overview on my brush collection, interested? Let me know :)
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| xo. |