Luggage makers always strive to respond to the growing demand from travelers for lighter and tougher suitcases. Their latest solution is baggage made of an ultra-lightweight yet highly durable material: polycarbonate resin.

The big surprise is that hard-sided cases have suddenly become popular again, now that they're as light as soft-sided bags. A 22-inch carry-on made of polycarbonate weighs a mere four-and-a-half pounds, the same as a traditional soft-sided piece made of nylon, and much lighter than traditional ABS hard-sided material. How light is four-and-a-half pounds? That’s light enough to hold a bag with your forefinger, when the bag is empty. Yet the plastic is still tough enough to avoid getting dented.

The glossy material isn’t new: Polycarbonate has successfully been used in motorcycle helmets, bulletproof glass and riot-police shields for a couple of decades now. In 2000, German luggage maker Rimowa introduced the material into luggage. Ironically, travelers were unnerved by how lightweight the luggage felt, worrying that it would prove to be flimsy, and the product didn’t catch on right away.

Yet sales of polycarbonate luggage recently began to take off in a big way, according to the Travel Goods Association. These suitcases are replacing old-fashioned cases at higher prices. Even Zero Halliburton, a luggage maker that’s famous for selling aluminum cases, says it is experiencing its strongest sales for its line of polycarbonate suitcases, such as the 19-inch Z-TEX (about $325).

Here are a few reasons to explain the current sales boom: Enough manufacturers have designs made of polycarbonate resin now that competition is bringing prices down from $800 a decade ago to as low as $140 now. Additionally, airlines have ramped up their fees for oversize and overweight luggage, so fitting everything into a single compact bag has become increasingly crucial.

Changing fashion is another factor. The polycarbonate material is eye-catching, because it can easily be dyed in brilliant colors, such as shiny tomato red, cobalt blue, and gleaming silver. Travelers seem to have become more willing to explore bold colours in their baggage. Black, which was the near uniform color choice of a decade ago, is today mixed with a wider array of hues and patterns, probably for the practical reason of speeding up identification of a bag in a pile at an airport carousel.

Budget Travel found a few types of the new luggage that are stylish, lightweight, sturdy and affordable:

Samsonite, the world’s largest branded luggage maker, showcases the Gravtec line of polycarbonate suitcases, imprinted with a raised-edge pattern. A 24-inch size model runs was recently for sale at $180 from ebags.com.

Britain’s Antler brand creates the Liquis 4 Wheeled Super Lightweight 22-inch carry-on, with a shiny and grooved polycarbonate outer shell in blue, red, or silver, with four multi-directional wheels at its base, recently from $299 at ebags.

Rimowa developed the technology to make polycarbonate luggage and today makes some of the chicest models, such as its Salsa 22-inch Globetrotter ($450 recently at Zappos). A zipper joins the two luggage halves in an improbable design, with four multi-directional wheels at the base.

All this news reminds me of the movie "The Graduate." Today, adults might tell kids that the future will be in polycarbonates.

More from Budget Travel:

• Vote! 15 places every kid should see
• 12 hot springs worth traveling for
• 10 hot new travel gadgets

Today a U.S. citizen received a prison sentence of two and a half years for breaking Thailand's "never bad-mouth the King" laws, reports the LA Times.

This case shows that foreign visitors to Thailand are not exempt from the country's laws against defaming the monarchy.

In this particular case, Thai-born Joe Gordon, a 55-year-old used-car salesman, wrote a blog posting several years ago — while he was living in Colorado — that included a Web link to a site featuring an unflattering biography of the king. Gordon then made the mistake last May of visiting Thailand for its famously affordable medical clinics.

Yes, he was jailed today for something he wrote in the US several years ago.

To be sure, Gordon's case is extreme, and the average American traveler's chances of being arrested abroad are only .006 percent.

But Gordon's case does underline an important point that affects all travelers: A few laws may be so unexpected that they can catch even culturally sensitive Americans off guard. In the case of Thailand, travelers may discover that police are obliged to investigate every complaint that someone has defamed the monarchy, and prison terms can last up to 15 years.

Here are four other surprising foreign laws to watch out for while vacationing abroad, based on reporting by journalist Katherine Spiers.

• Over-the-counter medicines in the U.S. are sometimes illegal in Japan, and that includes some Vicks and Sudafed products and anything else containing pseudoephedrine. If authorities at customs catch you with such products, they may detain you.
• Singapore puts a great deal of effort into keeping its public toilets (along with many other things) pristine. And visitors are expected to help keep them gleaming. Failure to flush may result in fines.
• Traveling by scooter in many major cities of the Philippines has its challenges: You can get ticketed for driving in sandals or bare feet.
• In Finland, taxi drivers playing music in their cars are required to pay a copyright fee. The idea is that the music is being presented to the "public" — the cabs' paying customers. So your cabbie might keep things quiet to save a few euros.

More from Budget Travel

• The weirdest hotels ever
• World's prettiest castle towns
• 10 most interesting beaches