6pcs Silicone Spill Proof Stopper Set, Reusable Leakproof Plug Spill Proof Straw Stopper with Straw Covers Seal Tumbler Accessory Compatible with Stanley Cup 2.0 40/30oz (Cream Yellow)

Seriously, not a single drop leaked!! I just put the parts in my tumbler and tested them by shaking the Stanley quencher upside down over the sink and not a single drop fellObviously it affects the flow of the water as air has to come in so you have to let go of the straw after each sip or two, but I don’t see this as an issue as I will mostly remove the middle part that goes inside the lid while using and place it back on when I need to put it in my back of the buggy’s basket.I’m actually astonished that Stanley hasn’t thought of selling these as an add on 🤯Never mind! Cheap works for me 😂 and it’s really working!!!

Good item but does not do the job 100%.

I bought this for my Stanley cup and it actually stops it leaking! Totally recommend

The straw top and hole cover are very effective, however the cap for the lid mechanism doesn't fit so well and always find it in my drink.

I only actually use the part that goes around the straw (filling in most of that large gap), and find this stops water splashing up onto my Stanley's lid while driving.I would recommend not using the round piece that attaches to the bottom of the lid, as this creates a blockage for air, which means drinking through the straw becomes more difficult and noisy. This is still worth the purchase without using that bottom piece.

Too big, didnt sit on straw.

Works at significantly reducing the amount of water spilling over but if help directly upside down it still drips.

Not spill proof.