Companies are developing alternatives to single-use plastic, and with options including seaweed and mushroom tissue, consumer interest isn’t disappearing, even during the coronavirus pandemic.

The coronavirus pandemic and fears about its spread have brought to a screeching halt years of efforts to get Americans to do one small thing: bring their own bags to the grocery store and stop using plastic ones.

California has allowed stores to use plastic bags until late June under an executive order from Gov. Gavin Newsom, even though the state has had a plastic-bag ban since 2016. New York delayed enforcement of its ban until June 15. Other cities and states have taken similar steps with backing from the plastic industry, despite evidence that the virus can survive longer on plastic than on other surfaces (like paper or cloth).

The pandemic came at a time when momentum was building for a shift away from plastic, with many consumers demanding alternatives or halting use of products (plastic straws) altogether. Although about 72 percent of Americans say they actively try to limit their plastic use, according to a 2019 Pew Research Center survey, the amount of plastic waste per person has remained constant: about 4 ounces per person every day, for a total of about 15.6 million tons in 2017.

But to those who are working on alternatives to single-use plastic, the consumer momentum is not disappearing. In fact, founders of several plastic-alternative companies said that they had seen even more interest from consumers in their products, and a renewed commitment from some of the larger companies they work with to press on.

"We’re fortunate enough that we aren’t seeing anyone say, ‘I’m not worried about sustainability, I’m just going to focus on survival right now,’" said Troy Swope, co-founder and chief executive of Footprint, which produces fiber-based alternatives to single-use plastics (cardboard, essentially). "If anything, we’ve seen an acceleration," he added, since companies often see a boost from using sustainable packaging.

Mr. Swope said that his product, which supplied food service items at this year’s Super Bowl, was different from other fiber-based alternatives in several ways. The most important are a shelf life that is comparable to that of plastic, which helps prevent additional food waste; complete biodegradability and compostability; and the ability to be microwaved, unlike plastic.

Footprint was born of Mr. Swope’s work for 15 years as an engineer at Intel, where he became an "accidental environmentalist." He saw firsthand the many different elements of plastic packaging that accompanied Intel products and was stunned by the amount of waste in the shipping and in the supply chain in general. He was even more alarmed that silicon wafers, elements of Intel’s processors, were considered contaminated after being transported in plastic that was similar to the tubs of cut fruit from the grocery store.

"We found the same level of contamination on the food that we did on the wafer," he said, adding, "if it’s bad for a wafer, it’s bad for a human."

Mr. Swope described a trip to Hawaii with Yoke Chung, his Footprint co-founder and colleague at Intel, many years ago where they realized that, because of ocean pollution and climate change, they were going to have to tell their children "what the ocean used to look like."

"So that combination of what we saw happening to the ocean, and the food contamination and, later on, what it was doing to our kids, made us say, ‘Let’s go do something about it.’"

Ocean plastic in particular has captured the public imagination, and seems to be a jumping-off point for several companies developing plastic alternatives, both in source material and in the pollution they are trying to prevent. One such company is Notpla, which uses seaweed extract to create its plastic alternative.

Notpla’s main innovation is a small pouch it calls Ooho, made from seaweed and other plants. This little pod (similar to a detergent pod), which is edible and biodegrades in four to six weeks, is the ideal replacement for single-serving condiment packets, said Pierre Paslier, the company’s co-founder and co-chief executive, who used to develop packaging for L’Oréal.

"We use plastic for five minutes, and it ends up in the ocean for 100 years," Mr. Paslier said, explaining the company’s interest in providing alternatives to plastic used for on-the-go foods.

Last year, Notpla partnered with Lucozade, a sports drink, to hand out capsules at an aid station at the London Marathon instead of single-use cups. The company achieved some moderate internet fame last year when Glenlivet, a Scottish distillery, unveiled whisky cocktails in edible Notpla pouches for a limited period, though seaweed is not a traditional whisky pairing. Notpla has also created a pouch for dry goods and a liner for cardboard food containers, which are often sealed with plastic and cannot be easily recycled or composted.

Different materials can leave consumers confused, and that inspired Zuleyka Strasner to found Zero, a single-use-plastic-free online grocery store. After a trip to a small island off the coast of Nicaragua where the shores were awash in plastic waste, almost none from the island itself, Ms. Strasner decided to try to live plastic-free for a year and a half.

She lugged reusable jars and bags to grocery stores, feeling self-conscious, she said. "I struggled a lot in those 18 months, and I was like, ‘Nobody is going to be able to do this; nobody is going to live this lifestyle if they have kids or a full-time job.’"

Like an old-fashioned milkman model "with supercharged technology," Zero Shop drops off groceries in reusable containers — mostly glass and silicone — which are then washed by customers, and picked up with the next delivery.

The company, which currently only serves the Bay Area with plans to expand, offers around 400 items, with everything from fresh produce and meat to chips and popcorn.

Ms. Strasner said that the company, somewhat surprisingly, had grown by about 200 percent week over week during the shutdown, and that consumers had not expressed concern about bringing reusable items into their homes. Fewer people, she said, touch her products than those at a grocery store, given the length of the traditional supply chain, not to mention indecisive shoppers.

Ms. Strasner does not use biodegradable and compostable solutions, favoring more permanent materials like glass and silicone. But decay can be productive, too: Ecovative Design uses mushroom tissue (mycelium) to create a packaging alternative.

Imagine receiving a television set in a box, its corners swaddled in plastic foam. Now, imagine that padding is made of mushrooms.

Ecovative grows packaging by filling custom-shape molds with agricultural residues like wood chips, which act as a food source, and mycelium cells. The mycelium feeds on the wood chips, growing its fibers around and through the food source, and, in four to six days, takes on the shape of the mold, which can then be removed.

Andy Bass, the chief marketing officer of Ecovative, said that the company was mostly "strain-agnostic" when it came to the mushrooms it used to produce its packaging, but that it had also developed its own strains for textiles and plant-based "meats." Ecovative’s incubators are set to particular temperature and moisture conditions, depending on the strain, which mimic conditions beneath the soil. This way, the mycelium "senses" that it is still underground, and grows only as mycelium fibers (the stalk of the mushroom), rather than as caps. The company has also used this technique to produce mushroom leather.

Ecovative develops its technologies and then licenses them to producers, who can then grow their own mushroom packaging or leather. As a result, it is not a consumer-facing company, so it has been less affected by the pandemic.

However, if the trend of home gardening during the shutdown continues, it could become a bigger part of our pandemic lives than previously thought: Ecovative’s mushroom packaging can be used as fertilizer.

In the end, it all comes full-circle, unless it’s plastic, which isn’t going anywhere.