Necessity is said to be the mother of invention but it almost sent this mom to an early grave.

One night, my teenage daughter and her friend were primping to go out when I found them rifling through a cardboard box stuffed with Chinese “Twin Lotus” condoms.

My heart stopping, my daughter pulled out a pair of scissors and began cutting them into strips. “Relax, Mom. We’re making Cuban rubber bands. I’m going to braid my hair.”

Cubans calls this “Inventando” — finding clever substitutes to life’s everyday shortages.

Days of the ‘fat cow’ long gone

An expectant father pulled apart an old sofa and used the wooden frame to make a crib. Another parent made her child’s birthday piñata from scraps of newspapers, recycled aluminum foil and wrapping paper she saved all year. A second-grade teacher encourages parents to bring in old work reports to replenish her supply of drawing paper.

People salvage just about everything here and consider very few things actual junk to be carted away in the trash. Many rural households even recycle old food and spoiled vegetables for animal feed.

In fact, where your average American produces almost 4 pounds of trash daily, Havana residents discard just under a pound.

This wasn’t always the case. There was a time when waste prevailed, years that Cubans nostalgically refer to as “La Vaca Gorda” — the fat cow.

Back then, the Soviet Union bestowed nearly $5 billion and 13 thousand tons of oil a year to the island.

Czechoslovakian buses polluted the capital, burning a gallon for every six miles of road. Construction brigades built bridges without connecting roads just to meet government-issued building quotas. Cuba’s massive state farms relied heavily on pesticides and chemical fertilizers.

That all changed in the 1990s when Moscow cut the purse strings, forcing the island to rethink conservation and people to resort to some truly inventive recycling.

Drive into any Cuban city and you’re assaulted with a political billboard urging environmental responsibility. “Water is life — don’t waste it” reads one. Another instructs “Conserve Electricity — use only what’s necessary.”

The ‘Gadget Guru’

On the outskirts of Havana, two icons make the typical Cuban neighborhood of San Francisco de Paula immortal — Ernest Hemingway, who once called it home, and Juan Martinez Rangel, who still does. To residents in San Francisco de Paula, both are local celebrities.

Neighbors call Martinez the “gadget guru.” For just pennies the retired machinist can transform an empty yogurt container into several electrical outlets, an old plastic dish drainer into a couple of water spigots.

A few years ago, when cooking gas regularly ran out, Martinez designed a backup stove to operate on either kerosene or gasoline. With no cash to buy a new refrigerator or fan, he built both from scratch. He even transformed a hydraulic truck lift he scavenged from the city dump into a machine that spits out plastic toys.

But that’s child’s play compared to his prize possession: “La Niña Bonita” — a jalopy-style car he assembled over a 20-year period with $70, a pile of scrap metal and junkyard parts.

A used tire supplied the brake pads, ¾ inch water piping provided the chassis, and old aluminum roofing furnished the body. He converted a motor from a Spanish water pump into the car’s engine, the carburetor and alternator were salvaged from a broken-down Russian motorcycle and the steering wheel was remolded from a discarded wheelchair.

“It runs like a normal car, goes forward and reverse, and can even get up to 42 miles an hour although I don’t like going that fast. It consumes too much gas,” complained Martinez. The vehicle gets 38 miles to the expensive $2.50 a gallon.

For the moment, Martinez doesn’t have to worry about rising gas prices. He keeps it parked in the middle of his living room after police ordered him to keep the unregistered contraption off the road.

Selling BBQs out the back door and cakes out the front

Oscar Millares is no different from millions of Cubans who went though a rough patch when the economy took a nosedive in the nineties. Like some 10 percent of the Cuban workforce, the electrician by trade gave up his government job when Moscow gave up on Havana, and started his own small business.

Using ancient tools including a century-old vertical drill, he welds outdoor barbecues, shoe racks and TV wall mounts from iron rods and discarded 55-gallon drums.

Business is brisk, he says. “My prices are a third of what the stores charge.” In part, that may be why he sells a bulk of his unlicensed products through the back door.

Oscar Millares sits in front of the industrial size food processor he is building from scrap metal and an old bicycle for his wife.

Last year, the Cuban government decided to put a brake on private entrepreneurs like Millares — despite a U.N. recommendation that the island’s centralized economy move in the opposite direction. The Labor and Social Security Ministry began turning down people requesting work permits in some 40 broad categories of employment including metalworkers, booksellers, clowns and flower vendors.

While the Cuban government would rather everyone draw paychecks solely from the state, Millares asked, “Who can survive on that income.” Selling just one of his outdoor barbecues earns him as much as he made in a month at his old job.

His wife plans to boost the family income another notch by starting her own sideline and selling pastries out their front door.