The blue ribbon is slightly thicker and therefore stronger, thinner and red is easier. Taking both bands together, one still has a difficulty level more. So can also be felt without weights exercises to perform with very high resistance.
Although the Rubber bands do not often used, but a few times as a handle for different exercises, or as a resistance band for different exercises. Here are the different strengths ideal supplement.
Edit: After approximately 1 year use the thinner red ribbon is in use. I think that's a shame, but it is understandable in the burden it had to endure. I ordered a slightly stronger band and am new to the remaining products continues to be very satisfied.