According to "Final Report of the International Space Station Independent Safety" (2007)
Russian windows have less meteoroid protection (less layers). Also there is no internal scratch to protect it from internal vandals, unlike the NASA/ESA design
5.11 Service Module Windows. Observations
The 13 SM windows are Russian-heritage hardware for which designers did not consider currently available data regarding MMOD in their design. The design consists of a two-windowpane (primary and secondary) configuration with the volume between the panes pressurized. This results in the external pane being the primary pressure pane. Unlike other windows on the ISS, most Russian windows do not have an external debris pane to protect against MMOD or an internal scratch pane to protect against damage caused by inadvertent crew activities. The probability of a critical failure (i.e., loss of a primary pane) is estimated by NASA to be one chance in six for all SM windows combined and one chance in nine for SM windows 1 and 2 over a six-year period. Loss of the primary pane would result in loss of redundancy in the window with respect to maintaining ISS atmospheric pressure. Early in the NASA assessment of the SM windows there were concerns that failure of the primary pane might cause failure of the secondary pane as well due to near instantaneous change in differential pressure since the volume between the two panes is pressurized. However, tests conducted by NASA using SM window hardware have demonstrated that the loss of the primary pane does not result in the loss of secondary pane.
Space station windows must also be certified to last at least 15 years.
However, the Service Module windows are based on the same design used for
the existing Mir space station and are designed to last 5 years. The Russian
space agency had not provided NASA with sufficient test data to verify that
the windows would last for 15 years, citing instead the fact that no windows
failed during the Mir's 14 years in orbit.
The glass used for windowpane is silica/quartz glass (http://www.sunhome.ru/journal/125924/p2 "«Для космоса» используется не обычное стекло, а кварцевое... марки СК и КВ (последняя — не что иное, как плавленый кварц) ... (КВ10С, К-108)"). There are several organisations involved in space glass development: "НИИ авиационного стекла Минавиапрома (теперь это ОАО «НИИ технического стекла») ... Государственный оптический институт им. С. И. Вавилова, НИИ резинотехнической промышленности, Красногорский механический завод ... Лыткаринский завод оптического стекла" (http://www.sunhome.ru/journal/125924/p1)