Squashy, shapeless and stuffed with recycled polystyrene beads, it's an unlikely contender for the year's must-have accessory. But, before long, I'll bet you'll find one nestling in the kitchens of Orlando Bloom, Leonardo diCaprio and every other celebrity with eco-credentials.
The Wonderbag, you see, is no mere style accessory. It might look like a Seventies beanbag, but it's actually a non-electric slow cooker. Tuck a pan of hot ingredients into its cosy folds, and it will keep them stewing slowly for hours.
Its inventor, Sarah Collins, 42, admits: 'It's the oldest technology in the world. I don't understand how someone else hasn't made it already.' Our ancestors buried hot stew pots in the ground to keep them cooking without fuel.
Our grandmothers tucked them into hayboxes - and I have a friend who swaddles pans of rice in her duvet when she goes to work. With the Wonderbag, Collins has simply brought the idea up-to-date and made it portable.
A South African eco-entrepreneur, she came up with the idea four years ago during a power cut, when she managed to keep her dinner cooking by surrounding the pan with cushions. The comical-looking prototype she later developed with a friend is already having a significant impact on the developing world.
According to scientists, each Wonderbag can prevent the emission of half a ton of carbon dioxide a year, and could save a poor family a tenth of their income by cutting fuel costs. Unilever has ordered five million Wonderbags for South Africa, and global companies Microsoft and JP Morgan have thrown themselves behind the goal of getting 100 million of the bags into our homes by 2015. This is all very laudable.
But as I'm not personally living in fuel poverty, I'm wondering just how relevant it can be to my busy urban lifestyle. At first sight, the answer is: not very. Patterned in lurid orange and green fabric, the Wonderbag squats on my kitchen surface like a giant pumpkin. The only member of the household who takes to it instantly is our cat, Marlow.
Not knowing where to put it (it's far too big for the pan cupboard), I leave it on the sofa and come back to find Marlow curled up inside. The Wonderbag comes with a recipe book, but you don't really need it.
The principle is simple: heat your food to boiling point for a few minutes on the stove in a normal saucepan, pop on its lid, then transfer it to the bag. It doesn't even matter how long you leave it there, because, says Sarah, it's all but impossible to overcook anything. 'I'm not a good cook,' she says. 'I don't want to worry about timings. I'm one of those people who just chucks everything in and goes away. But the Wonderbag has turned me into a good cook, because everything comes out so tasty.'
You can even leave rice in to cook overnight without it turning into sludge, she claims. It sounds too good to be true. I'm feeling sceptical as, after breakfast, I brown onions and beef in a pan with a tin of tomatoes and a bag of mixed veg. Normally, I'd simmer such a stew in the oven for hours. This time, I heat it for just 30 minutes before transferring the lidded pot to the bag.
Pulling the drawstring tight, I leave the house.When I get back home with the children, eight hours later, I'm frazzled. This is the most stressful part of my day, when, already tired, I help with homework while trying to whip up a balanced meal that won't elicit a chorus of yuks. No wonder I rely so heavily on pasta. But, as I open the front door I notice a delicious savoury smell filling the house.
Amazingly, inside the Wonderbag, the stewpot is still toasty. The chunks of beef are tender and the potatoes and carrots are cooked to perfection, swimming in a fragrant sauce, none of which has evaporated. Within moments, the children are sitting down to the sort of delicious, slow-cooked meal that I it thought was only possible to make at the weekend.
Meanwhile, I shut the lid and place the saucepan back in the bag to stay warm. An hour later, my husband and I finish off the stew. (I usually have to cook two separate meals, since he doesn't want to dine on my children's cold fish fingers). I am relaxed, and my hob is still clean. It's at this point I really begin to appreciate the Wonderbag's possibilities.
After dinner, I pour boiling water over a pan of oats, shove on the lid and stick it in the bag. My daughters like porridge for breakfast, but with the daily scramble for satchels, shoes and snacks, I usually manage to burn it. This time, breakfast is a breeze. We sit down to smooth, creamy porridge.
I feel so inspired that, before I go to work, I heat up a bag of pre-chopped vegetables in some stock and leave it to cook in the bag. The children don't even whinge when they find they're getting vegetable soup for supper, because they're so excited by the thought of food from the 'magic bag'.
The whole venture leaves a pleasant taste in the mouth. And, at £35, it's clear the Wonderbag will save me money - and every bag sold in the UK also funds a free bag for a needy household in South Africa.
For me, the savings are not just about fuel costs. It's that I can do the cooking in the morning, when I've got spare energy, rather than at night when I haven't, thereby reducing our consumption of expensive takeaways.
Plus, if we're out for the evening, I can lay on a healthy, slow-cooked meal for my teenage stepson without him having to use the hob - saving me the worrying that he'll have burnt the house down.
Although the Wonderbag was designed to help the poor, it's just as useful for those who are more short of time than money. 'I'm amazed by the uptake in the UK,' says Collins. 'It's not just people who are worried about green issues, we're getting busy executives and working mums. Taxi drivers love it because they can keep food hot all day in the cab.'
The bag can also keep food chilled, too, so it's great for summer picnics. So, just 24 hours after getting the Wonderbag, I can't imagine life without it. Of course, nothing is perfect. The bag itself is not currently recyclable because of the polystyrene beads used in it. And the fabric clashes horribly with my soft furnishings. I'm not surprised Collins has been advised to bring out a Wonderbag in Cath Kidston material to appeal to British tastes.
But I notice there is already a rather chic limited-edition spotty design on the website for £70. And real style purists can get a bespoke bag in fabrics to match their interior decor. So I'm going to snap up my own Wonderbag, before the waiting list gets as long as for a Birkin bag.
Ice and fire