It is as with all vacuum cups that are available: It depends on the cleanliness of both surfaces. When they don’t stick good enough, you should clean the surfaces. So, try the following: 

1. Remove rosin dust and hand sweat from your fingerboard

2. Wash the ResoundingFingerboard with clear and lukewarm water. You can use mild hand soap or mild hand dish soap (no aggressive ones!) and dry it with a dishtowel. 

A Trick
How often did the vacuum cups of our portable navigation device holder fall off while driving, or the cable of the antenna? It is as with all vacuum cups: with a bit of moisture they stick much better. String players fortunately have often experienced what it means having moistured fingerboards. If you avoid putting the fingerboard under water, you can smoothly moisture the vacuum cups from the inside. 

Avoid
No machine wash, dishwasher, no boiling water, no heating, no freezing, no keeping in the fridge. Extreme conditions destroy the functionality and the material itself. 

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