Rather than fitting completely into one mold or another, most investors are attracted to a blend of stocks, with some qualifying as growth investments and others meeting value-based criteria. Today, I'm taking a closer look at a few promising companies that belong firmly on the growth side of the spectrum. 

Sure, these stocks have soared higher in recent months as investor confidence in their businesses has grown. But in my view, lululemon athletica (NASDAQ:LULU), Wayfair (NYSE:W), and iRobot (NASDAQ:IRBT) have plenty of room for additional long-term gains.

Lululemon stretches higher 

Lululemon, the premium-sports-apparel specialist, has been putting up some head-turning operating numbers recently. Sales growth soared past management's targets for the second time in a row last quarter, with revenue jumping 19%. The gains came from both its physical and online store channels, and they also coincided with significant profitability improvements. Gross profit margin leapt to 55% of sales, in fact, from 51% a year ago.

People doing yoga in a studio.

Image source: Getty Images.

That success tells investors a few important things about this business, beyond the fact that its industry is expanding quickly. Lululemon appears to have strong customer loyalty, for one, as evidenced by its growing market share. The retailer's latest product releases are resonating with shoppers, too, who are gladly paying full price for its yoga-themed apparel.

Lululemon can lean on those competitive advantages as it pushes toward its goal of $4 billion in annual sales by 2020. That target seems easily achievable now, and the long-term picture could be much brighter as it expands to new geographies and outside its core, female demographic.

Wayfair aims for profits

If there were any remaining doubts that shoppers would warm up to the idea of buying home furnishings online, Wayfair put them to rest recently. The e-commerce giant has expanded sales at a 40% or better rate in each of the last three quarters. Other key metrics, including repeat-order volume and average spending per order, are also trending sharply higher.

The best news for investors is that Wayfair managed to improve its gross profit margins at the same time, even though rivals have been doing all they could to try to halt its market-share momentum. The fact that they haven't succeeded implies robust competitive strengths, particularly around pricing and customer satisfaction, for the upstart.

Wayfair is still losing money overall, since management has decided to pour all available resources into expanding into international markets while building up a huge delivery and technology infrastructure in the U.S. Those costs will eventually come down, though, at which point Wayfair could begin producing impressive earnings as the leading home furnishings e-tailer. 

iRobot is cleaning up

As the current market leader, iRobot arguably stands to lose the most as the robotic-cleaning-device niche moves into the mainstream. A flood of competition, particularly from low-priced rivals, could eat away at its dominant market share while sending profit margins lower.

Yet iRobot continues to defy that bleak outlook. Sales jumped 24% last quarter even as plenty of new rival products entered the market. Profitability improved, too.

A robotic vacuum cleaner sweeps the floor.

Image source: Getty Images.

With its intense consumer focus, a lot is riding on the upcoming holiday shopping season, which will determine whether iRobot meets its goal of passing $1 billion in annual sales for the first time this year. Its long-term outlook could be far larger, though, as a projected 86 million homes will eventually employ robotic cleaning devices, up from just 15 million today.

iRobot is taking the first step toward that larger goal with its new 7-series Roomba devices that, through innovations like automatic emptying, can clean for weeks without needing any input from users.

All three of these stocks are priced at premiums to peers, as investors have sought to incorporate their market-thumping growth rates into their valuations. That raises the risk of a sharp drop if performance declines. Still, investors who can stomach the volatility might be rewarded with outsized returns by sticking with these attractive businesses over the long term.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.