Every search for homemade eclipse glasses is really a search for a way to look at the sun today without having planned ahead. The honest answer is that there is no household material that filters sunlight safely for direct viewing, and the reason is that the dangerous part of sunlight is the part you cannot see.
Why the household materials do not work
Smoked glass, exposed photographic film, compact discs, mylar food packaging and stacked sunglasses all darken the visible image, which is what makes them feel like they are working. None of them is specified to block infrared, and infrared is what cooks the retina. A filter that makes the sun comfortable to stare at while passing heat is more dangerous than no filter at all, because it removes the discomfort that would otherwise make you look away.
What the injury actually is
Solar retinopathy is a thermal and photochemical burn of the central retina. It is painless, because the retina carries no pain receptors, and it usually becomes apparent several hours later as a blurred or blank patch in the centre of vision. It can be partial and it can be permanent, and there is no treatment that reverses it. The absence of pain during the exposure is exactly why homemade filters cause injuries: nothing tells you to stop.
The safe alternative, which is not expensive
A certified solar viewer costs about the price of a coffee, and the way to buy one safely is to buy from a supplier the American Astronomical Society has checked rather than to trust the ISO marking on the packet. If you have no viewer and the eclipse is today, the safe method is indirect: a pinhole in card projecting an image of the sun onto a second card, viewed with your back to the sun. It costs nothing and it cannot hurt you.
Questions people ask about eclipse glasses
Can I make eclipse glasses at home?
No. There is no household material specified to block the infrared component of sunlight, and darkening the visible image without blocking infrared makes the situation more dangerous rather than less.
What about welding glass?
Shade 14 or darker is genuinely safe for direct solar viewing, but shade 14 is uncommon in ordinary welding supplies and lower shades look comfortable while being unsafe. It is a poor bet against a purpose-made viewer costing a few pounds.
What can I use instead right now?
Pinhole projection. Make a small hole in a piece of card, stand with your back to the sun, and let the light fall on a second card. You are looking at a projected image, never at the sun.