a glass composition for glass bubbles used as reinforcing fillers in plastic resin articles has an improved compressive strength and the reduced alkali amount leached from the glass . the glass composition consists essentially of , by weight percentages , sio 2 40 - 59 %, r 2 o 2 - 17 %, r 2 o being at least one selected from li 2 o , na 2 o , and k 2 o , b 2 o 3 1 - 25 %, ro 5 - 25 %, ro being at least one selected from cao , mgo , bao , zno , and sro , ro 2 6 - 40 %, ro 2 being at least one selected from tio 2 and zro 2 , al 2 o 3 0 - 13 %, p 2 o 5 0 - 3 %, and so 3 0 . 1 - 1 . 0 %.