Clear Plastic

My Costume Idea Is A Lava Lamp. I Want To Use Some Sort Of Clear Plastic Material For What Would Be The Glass Of A Real Lava Lamp. It Doesn't Have To Be Extremely Sturdy, But Should Hold Its Shape. What Material Could I Use For This And Where Could I Find It? I Was Considering A Clear Acetate Film, But I'm Not Sure Where To Find That. Any Suggstions Would Be Greatly Appreciated.