Can these be used indoors? I'm building a gym and want to protect my floor and muffle the sound when I drop weights (250+lbs).

You can use our PlaySafe Interlocking Playground Tiles indoors. Even though these tiles are very shock absorbent, they are not the best flooring option for a gym. To help mitigate sound and also stand up against dropping weights, we recommend using our 1-1/4" Fit Rubber Tiles, which are interlocking, or our 1" Monster Tiles.