What is a good replacement for old glass storm window?
Our grand parents house from 1970's has these glass layers that sit outside the window frame, they replace them with mess layers during summer and use glass ones during winter. I believe they are called storm window! It's just one layer glass fitted into a thin aluminum frame. The glass is cracked, I am thinking to replace them with something durable, lighter than glass but withstand Midwest weather.
Any recommendations on best alternatives and where to get them? Should be clear and transparent like glass but stronger and light in weight so grand parents can handle it without breaking the storm window or their back.
Thanks!