Fiberglass is a type of fiber reinforced plastic where the reinforcement fiber is specifically glass fiber. Insulation is generally measured in R-value. R meaning resistance to heat flow. The higher the R- value the longer you retain your heat. If you have an R-19 the heat will stay 19 times longer than without insulation… R-30 will be 30 times longer and so on. There are a wide variety of brand names of insulation and all are the same for thickness and quality. Most companies use a dye to make it identifiable.