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"The new cup will have a two-piece valve that can be used with different types of liquid, and is easier to clean," the company said.

"In the meantime, we are making the transparent, see-through valves shown here immediately available to parents that have concerns. The see-through valve will enable parents to see inside, and give you confidence that the valve is clean.

"Alternatively, we will be happy to provide you with a different style cup if you prefer. Either option will be provided free of charge."

In a Feb. 24 Facebook post, the company said they "have extensively tested the valves using recommended liquids and ... specific cleaning guidelines."

They said the results of the tests support that "when used and cleaned in line with instructions, everything is in order."

The company has previously said that thicker liquids, like thick formula or pulpy juice, are not recommended for the cups because they can contribute to mold.

Related: Moldy sippy cups have parents disgusted and angry

"When used with recommended liquids (cold, light fluids including water and non-pulp juices) and cleaned in line with instructions, there are no problems," the company said.

But some parents complained that they still found mold even when they followed the instructions for cleaning.

Others said they cracked open the top and found no mold at all.

Read the full statement from Tommee Tippee on its new sippy cup tops below.