Gather 'round, children, and I'll tell you a tale of long ago, when coffee cup lids were designed to prevent coffee from spilling.

One day, the evil Grand Vizier whispered in the Sultan's ear: "Sire, coffee cup lids are badly designed. When in place, they prevent people from drinking coffee."

The Sultan was distressed to hear of this. He himself only drank from fine china, but he cared deeply for the welfare of his subjects. The Masters of the Guild of Coffee Cup Lid Manufacturers were summoned, and, after the customary obeisances, a proclamation was read: "Henceforth, all coffee cup lids shall be pierced with a hole, so that coffee may be drunk freely, without removing the lid."

Coffee consumption rose, and with it punctuality and productivity. GNP increased, and with it, the tax base. The Sultan Saw that It Was Good. Anyone carrying a cup of coffee had to move cautiously, to avoid splashing through the hole. The Paper Towel Manufacturers, Dry Cleaners, and Upholsterers guilds paid the agreed-upon bribe to the Grand Vizier.

In short, old-style lids (first link) had no hole, and were removed before drinking; new-style lids (second link) are designed for drinking with the lid in place, and have a hole. This is supposed to give the best of both worlds -- drinking without spilling, but it doesn't: when I walk briskly holding such a cup, coffee splashes through the hole.

I propose the addition of a baffle underneath the hole in the plastic coffee cup lid, to prevent splashing when the cup is jostled, while permitting a gentler pouring action by tilting the cup. Picture a flat, horizontal bit projecting inward from the lid circumference, a few mm beneath the hole.

An easier-to-manufacture solution is shown in the third link -- yet this is not widely used . (That's my impression, and a Google Image search on "coffee cup lid" (no quotes) supports this.) I believe the reason is that the lid in the third link isn't as comfortable to drink from.
-- mouseposture, Jun 12 2010

Old-style http://www.moma.org...e_id=1&sort_order=1
Notice whose website. [mouseposture, Jun 12 2010]

New-style http://www.freepate...7111749-0-large.jpg
A bit like sucking on a teat. [mouseposture, Jun 12 2010]

Another way http://hiatas.com/?p=186
Why is this not more widely used? [mouseposture, Jun 12 2010]

I believe the mechanics of spilling differ between driving and walking, which may explain the suboptimality of standard cups for walking: Spilling while driving occurs either because the cup is off-horizontal (the driver's eyes being on the road, not the cup), or a single large-amplitude horizontal jerk. Spilling while walking occurs when rhythmical vertical jostling sets up resonant sloshing. I think this is why even a partly-filled cup will splash up through the hole if I walk briskly.
-- mouseposture, Jun 12 2010



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