Flat glass prices edged down 0.1 percent in May, following a 1.1-percent dip in April and a 0.8-percent spike in March, according to the latest Producer Price Index Report (PPI) issued by the U.S. Labor Department.

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 123.0, and prices are up 1.9 percent from May 2014.

In another report, import prices for glass and glassware increased 0.2 percent in May, matching April’s slight bump. Prices in that category have increased slightly in each of the past four months but are down 0.1 percent from May 2014.

Export prices for glass and glassware, meanwhile, decreased 0.3 percent in May for the second straight month. Those prices, however, are up 0.2 percent from this time last year.

Prices of materials for construction continue their up-and-down trend of 2015, having dipped 0.3 percent in May. They saw an increase of 0.4 percent in April after dropping by that same rate in March. Prices in that category are up 0.6 percent from May 2014. Final demand for construction rose by 0.1 percent for the fourth straight month. Those prices are up 1.8 percent from a year ago.

On the whole, the PPI for final demand jumped 0.5 percent in May, seasonally adjusted, after falling 0.4 percent in April and increasing 0.2 percent in March. On an unadjusted basis, the index for final demand decreased 1.1 percent for the 12 months ended in May.

Overall prices for U.S. imports spiked 1.3 percent in May, marking the first time they haven’t decreased in 11 months. Export prices rose 0.6 percent in May after dropping 0.7 percent in April.