The inide of a bowling ball is mostly made up of resin, but there are many other elements too. Inside a bowling ball is a metal sphere which gives the ball more weight. Some balls can be seven kilograms in weight ( That’s heavier than my dog!). There is also another element which gives the bowler the power to spin the ball, this sits in the top half of the ball. There are also other things to make a bowling ball such as plastic but the weight is probably the most important.