▁is ▁added ▁to ▁increase ▁the ▁strength ▁of ▁the ▁glass , ▁or ▁as ▁a ▁flux ing ▁agent ▁to ▁decrease ▁the ▁mel ting ▁temperature ▁of ▁sil ica , ▁which ▁is ▁too ▁high ▁to ▁be ▁easily ▁worked ▁in ▁its ▁pure ▁form ▁to ▁make ▁glass ▁fib ers . ▁ ▁The ▁highly ▁bor on ated ▁glass es ▁used ▁in ▁fi berg lass ▁are ▁E - glass ▁( named ▁for ▁" E lect rical " ▁use , ▁but ▁now ▁the ▁most ▁common ▁fi berg lass ▁for ▁general ▁use ). ▁E - glass ▁is ▁al um ino - bor os il icate ▁glass ▁with ▁less ▁than ▁ 1 % ▁w / w ▁alk ali ▁ox ides , ▁mainly ▁used ▁for ▁glass - re in for ced ▁pl ast ics . ▁Other ▁common ▁high - bor on ▁glass es ▁include ▁C - glass , ▁an ▁alk ali - lime ▁glass ▁with ▁high ▁bor on ▁ox ide ▁content , ▁used ▁for ▁glass ▁st ap le ▁fib ers ▁and ▁ins ulation , ▁and ▁D - glass , ▁a ▁bor os il icate ▁glass , ▁named ▁for ▁its ▁low ▁Die lect ric ▁constant ). ▁ ▁Not ▁all ▁fi berg lass es ▁contain ▁bor on , ▁but ▁on ▁a ▁global ▁scale , ▁most ▁of ▁the ▁fi berg lass ▁used ▁does ▁contain ▁it . ▁Because ▁the ▁u bi quit ous ▁use ▁of ▁fi berg lass ▁in ▁construction ▁and ▁ins ulation , ▁bor on - cont aining ▁fi berg lass es ▁consume ▁half ▁the ▁global ▁production ▁of ▁bor on , ▁and ▁are ▁the ▁single ▁largest ▁commercial ▁bor