These cups are really adapted to their function. Silicone is firm but fair enough flexibility to allow their implementation. IF it was more flexible it would not hold when one must move! Compared to glass cups (which are hard), they put themselves back in place and at will, easily and without the drawbacks of their namesakes glass. Remember to oil the skin before. Usual manipulative I strongly advise locals and professional and beginners (who will need to gain some practice but it comes quickly).
