Latvian Devonian period sand from deposit Bāle and Jurassic period sand from deposit Skudra were studied, treated and compared with sand from existing Lithuanian supplier. Investigations of Latvian quartz sand showed that sand is characterized by surface impurities, which are easy to separate combining milling and water purification. These investigations and experimental glass melts using different types of sand confirmed that it is possible to use Latvian refined sand in glass industry. Other glass raw materials – colemanite, kyanite, kaolin, limestone – also have been examined. Glass fibre breakage points were studied using SEM, FTIR and X-Ray diffractions methods. Main reasons of glass fibre breakage are non-homogeneous glass and crystalline or gaseous inclusions coming from corrosion of refractory material. This article is result of the cooperation between Institute of Silicate Materials of Riga Technical University and JSC Valmieras stikla šķiedra.