Wood-pulp prices are soaring thanks to speculators in China, with help from paper takeout containers, a weaker dollar and people using restrooms at home instead of at the office.

Bleached softwood kraft pulp futures have risen 48% on the Shanghai Futures Exchange since Dec. 1, to about $1,037 a ton. Meanwhile, producers around the world are boosting prices for the wood mash at unusually sharp rates. Domtar Corp. , based in South Carolina, said it would raise prices this month between $100 and $130 a ton, depending on grade.

“Spot prices are really jumping,” said Brian McClay, a pulp-market consultant and a founder of pricing service Trade Tree Online. “I’ve been in the pulp business since 1978 and have been asking friends: No one has seen this before, no one has seen the scale of this.”

Prices are hottest for softwood pulp, the type that comes from coniferous trees and is used to make products such as premium toilet tissue, paper towels, junk mail and coffee cups. It is made from sawmill scraps as well as from trees too skinny, knotty or crooked to be cut into lumber.

China buys more than one-third of the world’s pulp and churns out paper products and packaging. Shanghai pulp futures, which began trading in 2018, serve as a price guide for an array of varieties and grades, similar to the way that West Texas Intermediate and Brent crude futures are reference points for oil prices.

wsj