Thickness 3.50mm Butyl Rubber Walls, Heavy Duty inner tubes with valve stems for kids bikes. These inner tubes are butyl rubber, which is more durable, thicker, and more shock-resistant than regular rubber, and provides a longer service life. These inner tubes are made from high quality butyl rubber, which is safe and non-toxic. The valve stem is made of premium steel and aluminum, which is durable, not easy to break or deform, and has a long service life. These bicycle inner tubes are suitable for Royalbaby, Huffy Kid & Joystar kids' bikes. These inner tubes are easy to install and remove. Please use tire levers to make your work easier and safer. These inner tubes are perfect for replacing damaged or flat inner tubes on your kids' bikes, and provide a safe and enjoyable riding experience for your children.