AULEEP Stress Balls for adults and Kids, 3 Pack Grip Strength Trainer Hand Therapy Exercise Balls, Anxiety Stress Relief Finger Resistance Exercise3 Different Resistance Stress Relief Balls The resistance levels of these stress balls include: Dark Blue (slightly soft); Grey (moderately hard); Sky Blue(firm hard), so you can choose the right one for your different needs. Safe and Durable Materials The outer material is made of tear resistant fabric, which makes the Soft squishy balls more durable. Inside of the balls are made of silicone gel. It dont have strong rubbery odor, theyre lightweight