Table:
|  | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, | Variation | Variation |
| --- | --- | --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 | 2019 vs 2018 | 2018 vs 2017 |
|  | (In millions) | (In millions) | (In millions) |  |  |
| Cost of sales | $(5,860) | $(5,803) | $(5,075) | 1.0% | (14.3)% |
| Gross profit | $3,696 | $3,861 | $3,272 | (4.3)% | 18.0% |
| Gross margin (as percentage of net revenues) | 38.7% | 40.0% | 39.2% | -130 bps | +80 bps |
Paragraphs:
In 2019, gross margin decreased by 130 basis points to 38.7% from 40.0% in the full year 2018 mainly due to normal price pressure and increased unsaturation charges, partially offset by improved manufacturing efficiencies, better product mix, and favorable currency effects, net of hedging. Unused capacity charges in 2019 were $65 million, impacting full year gross margin by 70 basis points.
In 2018, gross margin improved by 80 basis points to 40.0% from 39.2% in the full year 2017 benefiting from manufacturing efficiencies and better product mix, partially offset by normal price pressure and unfavorable currency effects, net of hedging. In 2018 unused capacity charges were negligible.
Question:
In 2018, why did the gross margin improved from previous year?
Answer: manufacturing efficiencies and better product mix, partially offset by normal price pressure and unfavorable currency effects, net of hedging.