NR foam, B 63, RG 350, fine-pored, open-celled, hard
Attributes: Foam rubber is a blown spongy-porous open-celled rubber that is produced from natural rubber (NR). Its good compressibility and elasticity, its ability to absorb and its surface adhesion all combine to guarantee that this oldest of all the blown rubber materials still finds many uses today.
Applications: Balls made of sponge rubber are actually used for cleaning pipes and tubes. They are also very popular however as representations of TREE CROWNS in architectural model making or also for use in the making of jewellery.
Using one of the larger balls (40 mm) in place of the horrible plastic ball that comes in a beachball set has proved to be a real delight. Because the balls have different levels of hardness they can be chosen so as to accommodate a fast or slow game. Plus they are so quiet when you hit them!
Treatment: Sponge rubber balls when used as treetops can be stuck on to a section of ABS tube (diameter of 1.2 or 1.6 mm) or round brass pieces to serve as trunks. It is of course easier just to stick them on STICKPINS or nails.
Sponge rubber and cellular rubber balls can be coloured by dipping them in thinned POSTER INK or TONING PIGMENTS whereby the white of the balls will still shine through. A similar effect can be achieved with SPRAY PAINT because it does not soak deep into the pores of the balls. A deeper colouration is achieved with the anthracite coloured sponge rubber balls because there the pores remain dark.