There has three resons:
Firstly:In order to reduce the viscosity of silicone rubber and pursue a good quality, you may add a lot of silicone oil into the silicon rubber when making molds. In fact, it might have just the opposite effect. The tension and the tear strength will be reduced badly with the addition of silicon oil. And the silicon molds will be in a weak and flimsy manner.
Sencondly:you may add too much catalyst into the silicone rubber,we suggest customers add catalyst no more than 5%,2%will be perfect.
Thirdly:you may use the silicone mold too early after it finished.we suggest the customer begin using the molds after 24 hours. whatsmore,it will be better if you can make a outmold to protect the silicone mold.