Gorilla Bow resistance bands (tubes) are mad from premium all natural latex and use a multi-layer technology to provide extra strength and durability. Resistance training is unique since the band tension increases the more you stretch it. Bands can, in some ways, be superior to free weights. Johns Hopkins Medicine recommends the use of resistance bands as one of the safest methods to increase bone strength and help reduce injury.
Here are specifications on Gorilla Bow Bands:
Note: The full tension is only achieved at full 2.5 times stretch. So if you have the 47" band stretched to 90" it will not be full strength. You will need to have it stretched to 118" for full tension. This is why you should use a higher tension band for exercises that require less stretch.