culvert balloon culvert balloon is used for making concrete pre-casting formwork projects in culvert bridge construction. Material: culvert balloon is made from natural rubber and fabric. In general, it is formed by three layers(1+2=2layers of rubber and 1 layer fabric): inner layer is high strength synthetic polymer fabric withstanding the force from concrete and air pressure. Outer layer is vulcanized rubber. Rubber hardness is about 65Shore A to keep its excellent features, such as soft, durable, wear-resistance. If your concrete slab is thicker, it should be manufactured in 2layers of fabric and 3layers of rubber(2+3). Standard specification 1-diameter from 0.2m to 3m,(round) 2-total length from 1m to 28m(round) 3-other specifications are also available according to clients’ request. Technical Parameters Items Index Thickness, mm 3.2±0.2(1+2) 3.7±0.2(2+3) Hardness(Shore A) 65±5 Adhesive tension of rubber and fabric,N/25mm ≥8 Tensile strength, M pa ≥12 Elongation at brea