The Hangar uses the String Swing yoke which is covered by a material that will not eat into the nitro of your guitar like most foams and rubbers do. Fender, Gibson, and Martin, all use the String Swing products in their showrooms, and for trade shows on their standard and high nitro finished guitars. However, there are some things that are out of our control that prevent us from putting an unconditional guarantee that no marking will ever occur. 1. If an issue does arise there is no definite way for us to tell if the marks were caused by our products or if they were from a previously used product from another manufacturer.   2. If you have used a guitar polish, be sure it is wiped off before you use our products. There is conflicting information on the internet as to whether polish is ever necessary or not. Also, along these same lines, do not use any chemical cleaners on our padding material. A damp cloth is fine if needed. 3. Guitars being stored in any sunlight can be a big problem, regardless of what material is being used in resting the guitar. 4. Nitro finish remains partially a liquid for its lifetime, so extended periods of time any significant pressure on the finish can result in pressure marks almost like a smear. This is worsened if the guitar was not given proper cure time when the finished was applied. All of this being said we still have the safest material on the market for a nitro finished guitar and thousands of people trust hanging them every day. Also, if you have a nitro white Gibson, or Epiphone we have white yokes that we recommend for these extremely colour sensitive finishes. If you decide to choose our products to display your guitars, for your peace of mind, we suggest that you check your guitars occasionally to be assured of their safety.