Yes, they contain a latex composite material.

When deciding on the right massage ball to buy, there are a few important factors to consider. This buyer guide will discuss the various aspects to take into account when shopping for the perfect massage ball set for you or your clients. We will focus on lacrosse balls, which are ideal for focused and deep-tissue massages. The size of the lacrosse ball determines how it is used for massage and which body parts it is effective for. NCAA lacrosse balls generally come in two sizes, a size 6 and a size 7. Size 6 balls are great for focusing on small areas like the sole of the foot or the nape of your neck, and size 7 balls offer a little more coverage for massaging large areas like your back or thighs. Size 6 lacrosse balls are also softer and are better for gentler massages that warm up and loosen tight muscles. Size 7 balls are harder and better for penetrating deep into tissue. The two most common materials for lacrosse balls that are useful for massage are rubber and foam. Rubber lacrosse balls are hard and have less give, making them ideal for deep tissue and hard-pressure massages. Foam lacrosse balls, however, are much softer and are great for light massaging or using your body weight to press the ball into your skin. Massages should be relaxing, so look for lacrosse balls without a chemical smell so you can create a welcoming and inviting atmosphere for decompression of your mind and your muscles.