Materials: silicone, stainless steel This is a closed helmet that can create a breathless breathing effect for choking bondage, but it is obvious that I cannot make it completely closed, which will cause serious consequences, so the remaining space of the collar and the gap between the two hemispheres are breathable. Note?Not suitable for claustrophobia patients. Helmet diameter is around 28cm-30cm,because it is handmade so can’t guarantee very precise size. Collar diameter has 2 options,12cm/14cm. Normally 12cm diameter Collar is for female, 14cm diameter is for male,just for reference. Due to the processing of metal materials, the closed helmet will have an odor, and it is recommended to use it after cleaning. Order parcel size 30*30*30cm,will be shipped by Post Mail which is cost-effective for this size parcel,it normally takes 7-27days for delivery,if you need expedited shipping option,it would costs extra fee,message me before order for inquiry. Recommended to use with the ball shape handcuffs in my store. https://www.bonanza.com/listings/Stainless-Steel-Ball-Shape-Handcuffs/1664127713