Mainstays 40 oz Double Wall Stainless Steel Tumbler

Mainstays 40 oz Double Wall Stainless Steel Tumbler scores 90/100 on Scout's independent analysis of ingredients, additives, and lab results — one of the stronger scores in Scout's catalog. Stainless steel is what touches the drink — inert food-grade steel that doesn't leach or shed microplastics.

Mainstays 40 oz Double Wall Stainless Steel Tumbler ranks #7 of 15 bottles, tumblers & mugs in Scout's independent rankings. The current top score in the category is UVBrite Water Bottle at 95/100.

In Scout's ingredient-by-ingredient analysis, Stainless steel (body) counts in its favor, and BPA-free plastic lid, spout or straw is flagged as an ingredient of concern. The full breakdown, with why each one matters, is in the Key ingredients section on this page.