An acrylic table top on patio furniture is a common substitute if you are replacing a glass one. There are some trade-offs when switching from glass to acrylic or fiberglass.
First, glass table tops are very heavy if you get tempered glass that is less breakable. However, glass is very strong and is almost scratch resistant.
Acrylic table tops are more easily scratched and you must be careful with what you use as a cleaner. They also can get tiny hairline scratches all over them from normal use.
Fiberglass table tops are very durable. If you get a solid finished one rather than clear, they are almost indestructible. They are also light weight.