Flat glass prices saw a slight 0.2-percent decrease in September after rising nearly 2 percent through July and August, according to the latest Producer Price Index (PPI) report issued by the U.S. Labor Department.

According to the report, flat glass prices are up 4.6 percent from September of last year and 4.4 percent over the last four months, thanks to a 2.8-percent spike from May to June.

The PPI program measures the average change over time in the selling prices received by domestic producers for their output, according to the U.S. Bureau of Labor Statistics (BLS). The prices included in the PPI are from the first commercial transaction for many products and some services.

The flat glass index sits at 127.4.

In another report, import prices for glass and glassware inched up slightly by 0.1 percent for the second month in a row. Prices in that category are up 0.2 percent from September 2014, with an index of 129.8.

Export prices for glass and glassware, meanwhile dipped 0.1 percent after staying flat in August. Those prices are up 0.2 percent from this time last year and have an index of 98.8.

Prices of construction materials were down 0.2 percent in September following a decrease of 0.4 percent in August. Prices in that category are down 1.1 percent from September 2014. Final demand for construction was stagnant in September and dipped 0.1-percent the month before, but those prices are up 1.8 percent over the year.

On the whole, the PPI for final demand dropped 0.5 percent in September, seasonally adjusted, after going unchanged in August. On an unadjusted basis, the index for final demand decreased 1.1 percent for the 12 months ended in September—the eighth straight year-over-year decline.

Overall prices for U.S. imports edged down 0.1 percent in September after a 1.6-percent decrease in August and a 0.9-percent dip the previous month. Export prices fell 0.7 percent in September after declining 1.4 percent in August.