Shoppers at Spreadshirt are increasingly mobile. 18% of traffic to the custom products e-retailer stems from smartphones and 7% comes from tablets—that’s double what it was only nine months ago, the company reports. When Spreadshirt begins marketing its new responsive web design site for tablets in June via paid search, online display and social ads, tablet traffic will quickly grow to reach 25% a year from now, the e-retailer predicts.

Half of Spreadshirt’s business centers on the custom design web tool on its e-commerce site. The other half of the business is supporting 45,000 web shops that operate on Spreadshirt’s e-commerce platform, which enables a consumer to design their own products and sell them in personally branded web stores.

Its e-commerce site is visually focused on designing custom T-shirts, but designs can be placed on any of 140 products, including hoodies, bottles, mobile phone cases, caps, bags and buttons. A consumer uses the “Design Your Own” tool that takes her step by step through the design process.

Spreadshirt decided to jump into mobile commerce through a responsive web design site. Responsive design uses one set of code and web content and displays content to fit the width of the screen on the device requesting a page. This is in contrast to building separate sites for tablets and smartphones. Spreadshirt staff had to rework the custom design tool for tablets because the tool was originally written in Flash, a web language that Apple Inc. mobile devices do not support. Now the design tool works on iPads, the dominant tablet computer.

But when it came to smartphones, Spreadshirt quickly realized that the screen was just too small for the custom design tool as it works today. So Spreadshirt prioritized creating the tablet version of the responsive site first and launched it in February. The e-retailer says it will launch the smartphone version of the responsive site with an optimized custom design tool in  the next 12 months. In the end, Spreadshirt will wind up with something of a hybrid—a responsive site with a few custom elements.

Today at Spreadshirt all eyes are on the tablet.

“There’s a difference between what a consumer is trying to do on a tablet versus a PC,” says Philip Rooke, CEO of Spreadshirt. “On tablets it’s based around browsing and experimentation, it is a longer consumer purchase. They will play on a tablet for an hour, but if they sit down in front of a desktop they have 15 minutes to achieve task A.”

Rooke notes that tablet traffic lights up when Spreadshirt broadcasts TV commercials. “When we do TV ads, that converts into tablet traffic extremely quickly because tablets are a second screen for consumers,” he says.

Spreadshirt built the responsive site in-house. So far it has cost the e-retailer $300,000 in labor; the final cost will depend on how much work is required to make the custom design tool work well on smartphones.

“We did it in-house because we have a very specific set of user experiences people go through, like create your own design or choose pre-existing design ideas, and we need to learn about those because we are also creating web sites for other people,” Rooke says. “We support 45,000 shops that use the white label of our platform and we have to turn those shops into responsive design sites as well.”

Rooke says all of the sites it supports will be responsive web design in the next 18 months.

“There’s a transition happening in e-commerce heading toward a majority of people having mobile as part of their shopping trip,” Rooke says. “Mobile has become a high priority for every e-commerce company in the world at this stage.”

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