By Julie Wernau

Tent suppliers across the country say they are inundated with calls from restaurants and retailers that hope moving business outside will lure customers as pandemic lockdowns ease.

High demand for tents and canvas is part of a wider boom for equipment and supplies, from plexiglass to hand sanitizer, that companies are buying or renting to protect workers and patrons from the coronavirus. That demand is raising revenue for some manufacturers, while increasing costs for restaurants and retailers preparing to open their doors again after weeks of greatly diminished sales.

In April, customers at 40 retailers, including Walmart Inc., eBay Inc. and Home Depot Inc., spent 47% more on party tents and event canopies than they did a year earlier, according to research firm Edison Trends. Public-health experts say that the likelihood of being infected by the virus is minimized when people are outdoors and appropriately distanced from others.

Delta Canopy Inc., which sells tents and canopies through retailers including eBay, Walmart and Amazon.com Inc., said sales are growing for the first time in five years.

"We usually do a lot of business at this time of year but it has probably tripled," said Amberly Slavens, assistant manager at the McKinney, Texas, company.

Blue Peak Tents Inc., a distributor in Illinois, Iowa and Michigan, said restaurants will be in competition with other companies that have rented tents for a place to screen employees for possible infection and to expand space for lunch and break rooms.

Gregory T. Parks, co-leader of law firm Morgan, Lewis & Bockius LLP's retail and e-commerce practice, said retailers are talking about adding space for outdoor shopping, including tented dressing rooms. Colleges, too, are considering using tents for classrooms. Amherst College in Massachusetts ordered 20 tents and Adirondack chairs, with plans to conduct some classes and activities outdoors.

"I'm glad we ordered them early," said Biddy Martin, Amherst's president.

Brady Castro, principal at PRO EM Party & Event Rentals in Phoenix, said some restaurants in Arizona want to extend seating capacity with temporary enclosures that include air conditioning. A basic canopy's cost per square foot is $1 to $2, he said, while that for an enclosed tent with air conditioning is about $10 to $12.

Chicago Alderman Brendan Reilly said his district, which includes the city's downtown, has 100,000 residents but hosts an additional 500,000 office workers and tourists each day during normal times. He said he hopes outdoor seating will help draw some of them back to businesses in his district that he said provide nearly a third of the city's restaurant jobs.

Mr. Reilly said he spent much of last week going block to block with a measuring tape and clipboard in hand, figuring out which streets in his district could be closed for outdoor restaurant seating.

Typically, establishing outdoor seating in Chicago takes months, as architectural renderings are subjected to bureaucratic reviews. Blocked-off streets in Mr. Reilly's district must leave room for a fire lane, bicycle traffic, wheelchair access and pedestrians. Now, the city is flooded with requests from restaurateurs who want to set up tents as soon as possible.

"If aldermen had it their way we'd close every street down to support the local businesses," Mr. Reilly said.

Kevin Boehm, whose runs Michelin-starred Boka in Chicago's Lincoln Park neighborhood, plans to start by opening just a few tables on the restaurant's patio. "What most people are grappling with right now is things like whether we'll have to take those tents down every night," he said. "They have to be secure."

Dean Zanella, chef and co-owner of Tripoli Tap, also in Lincoln Park. said he is planning to rent a tent to cover the restaurant's patio. He used to cram 50 people into that space on nice summer days; starting Wednesday, he will seat eight tables at a time with a minimum order of $20 a person.

Mr. Zanella is waiting for his neighbors to sign off on the giant tent he found to cover the space.

"We are doing everything we can," he said.

Write to Julie Wernau at Julie.Wernau@wsj.com