The value which most affects the accuracy of the hydrogen maser is the experimental determination of the frequency shift produced by the collision of the atoms with the surface of the storage bulb. In the current method of using different bulbs with various sizes in order to determine the frequency shift, a large amount of uncertainty is due to the unreproducibility of the FEP Teflon coatings from one bulb to another. A way to get rid of this error is to use a single deformable bulb whose volume can be changed while the same surface is retained. Such a bulb has been developed which can be adapted to any regular maser.